Sniffing and licking components of amphetamine-induced stereotypy were studied separately during chronic drug treatment. Sniffing showed a gradual increase, or sensitization, in intensity and duration. By contrast, licking developed tolerance for approximately the first 21 days, followed by a progressive increase. Stereotypy is therefore not a homogeneous phenomenon, and sniffing and licking are probably subserved by distinct neuroanatomic substrates. The sensitization of sniffing behavior may be related to the induction of amphetamine-induced paranoid psychosis in humans.