Brian Wilson has said of "Marcella": "It represents one of the first times we tried to emulate The Rolling Stones. In my mind, it was dedicated to the Stones, but I never told them that. It's one of the rockingest songs I ever wrote." According to Jack Rieley, the tune was named for a woman who was working as Brian's masseuse at the time. He explains:
...About that time Brian began talking in detail about a massage parlour in West Hollywood and one of the girls who worked there. At first he spoke only of going there for massages. Some days later he began going on and on about the masseuse who he said was turning him on.…The only thing I could think of to quell Brian's fixation was to channel it. Thus it was I who suggested Marcella as the title for a tune Brian had been working on. With my promise to write the Marcella lyric, he jumped into the project with immense enthusiasm. Brian, Carl, Desper and I worked hard on that record. Dennis helped too. The zither was a cool idea but it was mixed poorly. My lyric was minor... efficient at best.
The vocal arrangement is characteristic for a Brian Wilson song, featuring various syncopated lines following each other, reminiscent of a post-processed tape delay effect.