I'm in Mission on a mission: to find out whether a night on the tiles, knocking back organic booze, results in a hangover-free morning after. After extensive research (24 hours in the city), I can confirm that San Francisco is the undisputed world centre for getting merry the green way. Organic food is old news in California; farms in the surrounding valleys have been supplying the city's restaurants and shops for decades. Things have moved on - to organic wine, beer, vodka, gin, saké ...

Mission District, home to a multicultural community of students, artists, wasters, and young professionals, seems a good place to start because it's one of the hottest night spots, crammed with bars, restaurants and live music venues. In grungy Mission, even the street art has a social conscience; the walls of Balmy Alley are covered in bright protest art murals.

My first stop is Elixir, opposite the Mission Dolores church, which gave the area its name. Elixir is one of the oldest saloons in San Francisco and a great example of how far the green movement has come from its hippy roots. It's a regular sports bar with red walls, glossy dark wood and TVs, but one that happens to sell organic beer, wine and vodka.

My city-wide search takes me next to Vesuvio, one of the original Beat hang-outs and next to the legendary City Lights bookshop. I take a seat at the bar and get chatting to the woman sitting next to me, Janet, who turns out to be one of the co-owners. She shows me her organic drinks menu, designed by the bar's artist in residence. There's Fat Tire beer from the New Belgium Brewing company, which uses 100% renewable energy, and energy efficient lighting; Bonterra organic wines; and organic gin, saké and vodka. The latter is Square One, an American rye vodka which comes in a recycled glass bottle and goes into lethal-sounding cocktails such as the Saketini.

Onwards to Millennium, a downtown vegan restaurant with a cocktail bar where the spirits are infused with organic fruits, herbs and nuts. It's got to be the healthiest way to get drunk; the tequila sunrise comes with orange juice, cranberry and a splash of pomegranate. I begin to suspect an organic hangover isn't going to be much better than a regular one and call it quits.

So, where does a tipsy green crash out? In an eco-hotel, of course. The newly opened Orchard Garden Hotel is the first in the state to be built according to the US Green Building Council's strict standards. The hotel was built from scratch, which means they were able to use environmentally friendly materials rather than "green washing" the rooms. It's not the most glamorous place in the city (that accolade probably goes to the St Regis or the Schrager-designed Clift Hotel), but it's central, affordable and the designers have succeeded in avoiding what manager Stefan Muhle calls the "hemp and muesli look".

The next day I'm a little bleary. An hour-long walk, taking in Russian Hill, which is still "nothing but laundromats, cleaners, soda fountains, beauty parlours" as Kerouac wrote half a century ago, brings me to Lettus, an organic cafe in the Marine district. It takes me 10 minutes to decide which smoothie to have - then I have to make another decision.

"Would you like bee pollen with your smoothie? It's, like, really good for you."

I'm not convinced, but I pay the extra 70 cents in the hope that it might give my jet-lagged, hungover, sleep-deprived body the boost it needs. Then I order some proper food - an egg bagel with cheese.

I like Lettus, despite the terrible pun. It's bright and breezy, the staff are sweet and friendly, and, apart from the odd whacky supplement, the menu is full of appetising dishes. If you're more of a hemp and muesli type, there's Café Gratitude, which specialises in raw food and where every item is prefixed by a positive statement; I would love to hear someone order the "I am open-hearted spicy mole pizza".

But on balance, the city that practically invented the hippy seems to have got it right. People genuinely care about what they eat and drink and about the environment, but most of all they seem to be having a good time in pleasant surroundings while they're at it.

· British Airways (0870 2433406, ba.com) flies London-San Francisco from £314 rtn. The Orchard Garden Hotel (theorchardgardenhotel.com) from $160.