Repeated amphetamine (A) or methamphetamine (M) treatment induces behavioral sensitization and drug conditioning. The present study compared behavioral sensitization and drug conditioning between treatments with M combined with scopolamine (S) and M alone with respect to a reciprocal balance between the dopaminergic and inhibitory cholinergic systems in rats. Repeated treatment with M (4.0 mg/kg i.p.) combined with S (0.5 mg/kg i.p.) (MS) produced progressive enhancement of stereotyped behavior, compared with repeated M treatment alone. Repeated MS treatment induced focussed stereotyped behavior that was elicited by every challenge injection of not only MS and M, but also partially by S. MS- but not M-sensitized rats exhibited conditioned responses to a tone (300 Hz, 100 dB) associated with drug state, suggesting that MS-induced pronounced behavioral sensitization may lead to an enhanced conditioned response to the conditioned stimulus (CS) of a tone. It is suggested that MS-induced behavioral sensitization may be mediated via a reciprocal balance between the dopaminergic and cholinergic systems in favor of a dopaminergic dominance, and that such a balance may be involved in the conditioning to the drug-associated tone CS.