Clients admitted to treatment centers for stimulant addiction were categorized as either regular users of cocaine or of methamphetamine based on an algorithm involving 5 specific criteria. A subsample consisting of 90 regular users of cocaine and nonusers of methamphetamine, and 39 regular users of methamphetamine and nonusers of cocaine, was selected for comparison. Analyses showed that, when compared with cocaine users, the methamphetamine users exhibited a shorter period of time from 1st use to regular use (period of initial use) and from 1st use to treatment entry (period of pretreatment use). Relative to cocaine use, the use of methamphetamine appears to induce a faster rate of progression toward regular use and subsequent need for treatment.