As gay and lesbian couples start to wed in California, businesses large and small prepare to pull in millions.

At Los Angeles' gay pride parade June 8, a local radio station had a float emblazoned with a banner that read, "Welcome to the hell that is marriage." The message was a cheeky nod to the May 15 California Supreme Court ruling legalizing marriage for same-sex couples, but it typified how quickly some segments in the business community are gearing up for same-sex nuptials, which began Monday evening.

Gay and lesbian couples are sure to be ecstatic on their wedding days, but the ones shedding the most tears of happiness may be California's wedding and honeymoon vendors. Will a change in law mean a bull market for big fat gay weddings? The Williams Institute at the U.C.L.A. School of Law thinks so. The think tank released a study June 9 showing California's $6 billion-a-year wedding industry will get an infusion of $683 million over three years in direct spending by same-sex couples.

Based on numbers in Massachusetts, where it has been legal for resident gays and lesbians to marry since 2003, the Williams Institute estimates roughly half of California's 102,000 domestic partners will get married, while another 68,000 couples from outside the state are expected to come and celebrate their nuptials. The Institute thinks same-sex marriage should generate 2,200 jobs in California, bring in $8 million in marriage-license fees, and increase sales and occupancy tax revenues by $55 million. A 2005 study showed that if same-sex marriage was legalized nationally, the wedding industry could generate another $2 billion annually.

That's peanuts for the overall industry, since 2.4 million straight couples get married each year and spend on average $20,000, racking up a total of $72 billion, according to bridal website theknot.com. But the potential for a deep-pocketed, underserved market coming online in an economy where more straight couples may be thinking of pulling back their spending is undoubtedly attractive to vendors.

The impact on California and the rest of the country could be significant, says Betsy Stevenson, an assistant professor at the Wharton School who studies the tax implications of marriage. She compared marriage in the Golden State today to Nevada 60 years ago, when that state's lax divorce laws made it a destination for couples looking to split. The revenue Nevada brought in encouraged other states to change their divorce laws. "Once California starts making money, other states will want to get into the game," Stevenson said.

San Francisco first saw the economic potential back in 2004. Thousands of same-sex couples were married out of City Hall around Valentine's Day before the state put the kibosh on the renegade licenses and began litigation that ultimately led to this year's decision. Businesses in the city, which for years have catered to informal commitment ceremonies, were struck by a "Flowers from the Heartland" phenomena, a movement in which well-wishers ordered wedding flowers for same-sex couples they didn't know. Thousands of bouquets were distributed randomly to the throngs of couples waiting to get married, a boon to florists in the city.

But this time around, the feeling is that marriage will be more lasting, said Joe D'Alessandro, the president and C.E.O. of the San Francisco Convention and Visitors Bureau. He and his partner of nearly six years are planning a 75-person wedding for Labor Day, with a budget of about $10,000. "That's the ballpark we've talked about," he explained. "It's easy to run up. You can go through that in a flash."

Expanding existing business without alienating the mainstream is a common theme, even if you're taking out full-page newspaper ads that seem to be congratulating same-sex couples. Less than two weeks after the California court decision, Macy's made headlines in San Francisco and Los Angeles touting its gift-registry program in an ad that read, "First comes love. Then comes marriage. And now it's a milestone every couple in California can celebrate." Macy's spokesman Jim Sluzewski resisted any suggestion Macy's was taking a stand on same-sex marriage, since all the company was doing was innocently running an "inclusive" ad that promotes its registry, which has been open to same-sex couples for 15 years. "The fact that we are advertising a wedding registry is not at all unusual," he said. "In the wedding business, everything is new business."

For businesses rushing out to buy rainbow-colored paraphernalia and bride-bride cake toppers in bulk in a bid to attract cookie-cutter gay nuptials, cool your heels, since same-sex couples are likely to be as individualistic as their straight counterparts, said Tegan Firth of San Francisco's Hornblower Cruises & Events. Her company has served same-sex couples for years, and in the first 10 days after the court decision got inquiries from 15 couples, half from outside California.

"Commitment ceremonies and now same-sex weddings are going to be similar to other kinds of social celebrations in the sense that it is a very unique experience for the individual," Firth said. "A lot of times the requests we receive are very specific to the couple."

Joie de Vivre Hotels is offering a promotion that is designed to appeal to socially conscious gay and lesbian couples. The boutique hotelier's Silicon Valley property Hotel Montgomery will donate 10 percent of any group block rate for same-sex marriage bookings to the Human Rights Campaign, a national gay-rights advocacy group that is gearing up to fight a statewide constitutional amendment initiative in November seeking to overturn the marriage decision.

The hotel group is also preparing an information packet for couples that includes courthouse times and other specifics visitors may not know, such as the requirement that you must be in California for at least 24 hours before getting married.

Susan Wilcox, the vice president of communications for the California Travel and Tourism Commission, put out a press release June 3 promoting venues beyond the traditional gay favorites that are also waiting to serve the happy groom and groom, such as locations in Yosemite and the Cascades.

Figuring out if estimates are correct that marriage is a financial gain for California is premature. "It's kind of hard to say what that will net out as," Wilcox said, noting economic impact numbers are "elusive statistics." But in this case, there will be a paper trail.

"At least with marriage numbers we'll be able to tell who came and what they did," she said. "We will know from the marriage licenses. All of those statistics will be very telling."

But for D'Alessandro, his marriage is more than just a statistic to him. "It is a basic civil-rights issue," he said. "The emotions are very powerful."