Research indicates that chronic daily cocaine injections produce sensitization to, while the chronic continuous infusion of cocaine produces tolerance to, its behavioral and neurochemical effects. The present experiments examined whether flupenthixol administration during withdrawal would attenuate/eliminate the behavioral effects produced by these administration regimens. The rats were pretreated for 14 days with either continuous or intermittent daily injections of cocaine, and were then withdrawn from the pretreatment regimen for 7 days. On days 1-5 of the withdrawal period, subjects received a daily 0.125-2.0 mg/kg IP injection of flupenthixol. Then on day 7 of withdrawal from the cocaine pretreatment, all rats were given a 15.0 mg/kg IP injection of cocaine. Their behavior was rated according to a modified version of the Ellinwood and Balster (6) scale for 60 min. The results indicated that flupenthixol treatment during withdrawal eliminated the tolerance normally associated with the continuous infusion of cocaine. However, this effect of flupenthixol was not dose dependent: the lowest dose had the same effect as the highest dose of flupenthixol. In the cocaine-injection subjects, flupenthixol had a slight but statistically significant reduction in the behavioral effects of cocaine. The same was true in the saline-control rats, except for the highest dose of flupenthixol, which had a significant enhancing effect on the behavioral response to cocaine. The present results suggest that the current procedures may represent an effective screening methodology for potential cocaine pharmacotherapies.