In this work, we studied the effect of low doses of intracerebroventricular corticotropin-releasing factor (CRF) in six sessions of forced swimming test (FST). When CRF (0.01 and 0.1 microg) was administered pre-test, results showed that the 0.1-microg dose significantly increased swimming in SESSION2, SESSION3 and SESSION4, while the 0.01-microg dose proved ineffective. When CRF (0.1 and 0.03 microg) was administered post-test to evaluate retention of swimming response, the dose of 0.1 microg impaired retention, while the dose of 0.03 microg improved it, although these effects only reached significance in SESSION2. In an additional session (SESSION6), testing long-term retention of this swimming response, the 0.1-microg dose significantly impaired retention, whereas the 0.03-microg dose proved ineffective. A high dose of CRF (1 microg) was also included as a control of previous results [García-Lecumberri C, Ambrosio E. Role of corticotropin-releasing factor in forced swimming test. Eur J Pharmacol 1998;343:17-26]. In all the FST sessions, this high dose increased swimming when administered pre-test, while impairing retention when administered post-test. Preliminary data obtained with low doses of CRF suggest that a differential effect on retention of swimming response seems to exist depending on the dose, whereas a high dose of CRF clearly impairs retention. The role of CRF in learning and memory processes in FST is discussed.