The still-faithful Deadheads, who paid as much as $1,000 each to join the Grateful Dead at the Great Pyramid Thursday night, are the last remnant of the Acid Test culture which flourished over a decade ago in San Francisco.

It was the Dead's eclectic commune on Ashbury Street, that served as the shrine of hallucinogenic exploration. It was the band's energetic mixture of rock 'n' roll, country lyrics and tran-scendental mysticism that swept the "flower children" into Ken Kesey's LSD experiments.

"It started with the Acid Test Rock Dances," recalls John Warnecke, the Dead's former road manager. "We'd advertise these big free dances in (Golden Gate) park every weekend. The Grateful Dead would play for a while and then disappear; then the Kool-Aid (spiked with LSD) would appear over at the side. The band would wait an hour or so till the acid took effect, then come back on stage and try to play."

"The basic feeling was that it was all for the people - that if we do it, we all do it together," says Warnecke. "It was, 'Let's explore the universe, let's go there together.' For every paid gig, we did not free."

It was a time, as Scott MacKenzie would sing in his anthemic "San Francisco," of "people in motion." Janis Joplin, young, raw and already drinking heavily, traipsed restlessly in and out of the Ashbury house; another frequent visitor was photographer Linda Eastman (now McCartney).

Then, as now, the charisma was hard to define.

"There was a lot of sex, if you want to say that, but the real trip was spiritual," says Warnecke. "We were really protective of each other - a family."

The Grateful Dead recorded their first album for Warner Bros. in 1967, but their cult following increased as much because of their legendary life style as their music. During a hectic two-week period in which an entire album's worth of songs was written, the band rehearsed on a stage built over a stream on their Marin County ranch, and for miles around, fans canoed down to listen.

As the '60s waned, the band's reputation grew, and taking the whole "family" on the road became a full-scale production. The Dead were known for their high-quality, high-volume sound, requiring hundreds of speakers (one 10-by-10-foot speaker provided a hiding place for friends who wanted to get high off the sheer thundering vibrations). By the early '70s, the band needed four semis to handle their equipment.

Riots followed them across Europe in 1972. A live Radio Luxumbourg broadcast, in an old castle-turned museum-turned station, reached nearly 100 million listeners; frantic Dead heads outside the castle smashed the windows.

The band's bypnotic presence, and the energy which careens between the Dead and the 'Heads,' cannot be captured on vinyl. The magic depends in part on the remembrance of acid shared - one of the band's friends speculates that a resurgence of LSD use has sparked a new wave of young Dead fans who never heard of the Fillmore.

In 1974, after nine albums with Warner Bros., the Grateful Dead founded an independent record company to control both recording and national distribution. The company is based, not in San Francisco, but in San Rafael, the Mecca of mellow Marin County. Their new album will be released next month.