Conditioned place preference (CPP) was employed to clarify the reinforcing and locomotor stimulating effects of several doses of cocaine and caffeine (0.32, 1.0, 3.2, 5.6, and 10.0 mg/kg) and to explore the possibility of additive effects between the two drugs. Additionally, the hypothesis that the reinforcing effects of psychostimulants are mediated by the same systems that control psychostimulant-induced locomotor activity was examined by conducting correlational studies between drug-induced locomotor activity and time spent in the drug-conditioned compartments. Several doses of cocaine (1.0, 3.0, 5.6, 10.0 mg/kg), and caffeine (0.32, 1.0, 3.2, 5.6, 10.0) were found to condition place preference and stimulate locomotor activity. A combination of low doses (0.32 mg/kg) of each drug appeared to be additive. A positive relationship between locomotor activity observed during conditioning and time spent in the conditioned compartment during testing was found for cocaine but not caffeine or the low-dose combination of cocaine and caffeine.