Catching their show one night was drummer Jimmy Chamberlin, himself the son of jazz musicians, who had been taught how to play by Yanni drummer Charles Adams at the tender age of nine. During his teen years, he absorbed a variety of jazz styles from big band to Latin. Also catching the show was the owner of Cabaret Metro, another club in town; he offered the band a gig if they got a live drummer. Through a friend, they invited Chamberlin; Smashing Pumpkins made its debut as a quartet on October 5, 1988.

After a little more than a year of gigging, the band released their first single in 1990, "I Am One" on Limited Potential records, a Chicago imprint. It quickly sold out its pressing, and their next single, "Tristessa" was released on Seattle's Sub Pop records, which was growing fast due to the success of their grunge acts. Sub Pop was attracting interest from major labels for almost any band on its roster in those days, and a bidding war for Smashing Pumpkins broke out. Virgin ultimately signed them, but kept the deal quiet; it was decided that their first release would be on the subsidiary label Caroline, giving the impression that they were recording for an indie label, thus helping them retain street cred.

Regardless, their debut album for the label, Gish, was one of the earliest shots of alternative rock in the modern sense to hit the public. Released in 1991, the album was produced by Butch Vig shortly before he'd produce Nirvana's Nevermind, and deserves recognition as perhaps the first alternative-rock album in the 1990's sense of the word. The album goes a long way in establishing what Smashing Pumpkins were all about; art rock and heavy metal on an arena rock scale, cut with a power pop perkiness. Corgan's lyrics were confessional, and bordered on obsessive. The arrangements are the first thing that strike the listener; ornate, textured, and layered, it recalled Brian May's work with Queen. While the album is an inconsistent listen, its best moments were standouts in that pre-alternative universe. "Siva" is an immediate grabber; "Rhinocerous" veers into lush dream-pop territory, "I Am One" is a brutal quasi-Black Sabbath riff fest. The album only made a token appearance on the album charts at #195, but was #6 on the Heatseekers chart; if Gish really was a major label release in disguise, the plan seemed to go off without a hitch.

There was a minor backlash; once the Caroline Records ruse was pieced together, indie purists accused them of being phonies. However, these charges failed to stick in the face of such good music; as formerly indie bands signed with major labels right and left, the very notion of "indie rock" was in tremendous flux. It was this redefinition of indie rock, by Smashing Pumpkins and Nirvana at the forefront, that led to the coinage of the phrase "alternative rock" to describe the phenomenon.