In view of potential ability of calcium entry blockers to affect Ca2+ fluxes in neurons, the effects of nisoldipine on phencyclidine (PCP) and apomorphine (APO) induced stereotyped behavior have been examined in 3 and 4 week old rats. The rats (3 and 4 weeks old) were pretreated with either 0.2 ml of saline + ethanol mixture (10:1 v/v) or nisoldipine (25 mg/kg) i.p., 5 min before the i.p. administration of PCP (5 mg/kg) or APO (10 mg/kg). While nisoldipine pretreatment significantly blocked the PCP induced stereotypy in 3 and 4 week old rats, the APO induced stereotypy was not altered. These preliminary data suggest that nisoldipine specifically blocks PCP induced stereotypy probably by antagonizing it effects at the presynaptic level. The significance of this finding in relation to mechanism of action of PCP and calcium entry blockers is discussed.