The pharmacokinetic interaction between chloroquine (CQ) and imipramine was investigated in six healthy volunteers who received 300 mg of CQ, 50 mg of imipramine, and combined doses of both drugs in a randomized, crossover design. Blood and urine samples were collected at predetermined time intervals and were analyzed for the drugs and their metabolites by high-performance liquid chromatography methods. The results revealed that the plasma concentrations of CQ and its pharmacokinetic parameters were not significantly altered when CQ was coadministered with imipramine (p> 0.1). The plasma concentration-time profiles and the disposition characteristics of imipramine also were not altered after coadministration with CQ. The results suggest that there appears to be no pharmacokinetic interaction between CQ and imipramine given as single oral doses.