In rats given methamphetamine (MAPT, 10 mg/kg i.p.) 24 hrs--48 hrs after the long term-administration of reserpine (RE), we have previously found such "bizarre-biting behaviour" as persistent and bloody biting activity at their own legs and tails or those of their cage mates. The present investigation examined the effect of a blockade of the dopamine receptor in the brain on MAPT-induced "bizarre-biting behaviour" and hypermotility of RE-pretreated rats. Male albino Wistar rats aged 4 weeks were injected intraperitoneally with RE (1.25 mg/kg) or 0.9% saline solution (1.25 ml/kg) every two days for 13 days. Twenty-three hrs after the last injection, rats received chlorpromazine (CP, 150 micrograms, 250 micrograms, 625 micrograms, or 1 mg/rat) intracerebrally by Valzelli's method; and 1 hr later, MAPT (10 mg/kg i.p.) was injected. MAPT-induced hypermotility was potentiated in the RE-pretreated rats, but it was suppressed dose-dependently by CP. Stereotyped licking and biting activities of saline-pretreated rats were completely suppressed by CP at each dose given, however, the "bizarre-biting behaviour" of RE-pretreated rats was inhibited by CP only at high doses (625 micrograms or 1 mg/rat). It is suggested that the MAPT-induced hypermotility of RE-pretreated rats is mediated by activation of dopamine receptor while their "bizarre-biting behaviour" is partially related to it.