Chlorpromazine and imipramine were administered to DBA/2J and C57BL/6J mice swimming in a Y water maze toward a light source (L Procedure, corresponding to innate tendency) or towards the dark (D Procedure, corresponding to the acquisition of a new pattern of behavior). In two sets of experiments the drugs were administered to naive mice before and after each training session, respectively. In both strains, in the pretrial experiments, the innate tendencies were improved by both drugs; the acquisition of a new pattern of behavior was improved following imipramine but impaired following chlorpromazine. In the posttrial experiments (D procedure) the consolidation processes of both strains were improved following imipramine and impaired following chlorpromazine. In a third set of experiments imipramine was administered to previously trained mice of both strains and chlorpromazine to previously trained C57 mice. In both procedures the administration of increasing doses of both drugs was followed by a progressive lenghtening of the swimming times in the previously trained C57 mice; performance disruptions were evident in both procedures in trained DBA mice mice following imipramine.