The development of sensitization to the behavioral effects of cocaine occurs with repeated intermittent usage. In the present study rats were given five daily i.p. injections of cocaine (10 mg/kg) immediately prior to placement in an open-field environment for 20 min to induce cocaine sensitization. Control groups received saline injections or cocaine injections (10 mg/kg) 30 min after testing in the home cage. One week later the animals were given a challenge test with 10 mg/kg cocaine. The animals that had received cocaine in the test environment exhibited a more rapid onset of cocaine-induced behavioral effects than either animals previously treated with saline or animals that had received cocaine in the home cage. In a second experiment, the same sensitization protocol was followed except that during the interval between the end of the cocaine/saline treatments and the challenge test, the animals were given six daily 20-min saline tests to assess the contribution of differential habituation and/or Pavlovian conditioning to the sensitization effect. Neither habituation or Pavlovian conditioning altered the more rapid onset of cocaine stimulant effects induced by repeated cocaine treatments. It is suggested that the faster onset of cocaine effects is another way in which cocaine sensitization contributes to cocaine abuse liability.