Modulation of CA1 electrophysiological properties (amplitude, latency, paired-pulse facilitation) by different concentrations of corticosterone (CT) was studied in hippocampal slice preparations from normal (sham) and adrenalectomized (ADX) BALB/c mice. In the sham group, CT effects on the population spike (PS) amplitude were biphasic: at a low dose (200 pM) CT induced a delayed increase; at a moderate dose (2,000 pM), a rapid and partially reversible decrease was observed, and at higher doses (5,000 and 10,000 pM) this decrease was more pronounced after 30 min of washout. Diminution of latency and paired-pulse facilitation were obtained for the CT concentration inducing an increase of the PS amplitude. In the ADX group, similar CT effects were observed for lower doses: a decrease of the PS amplitude was observed for 40 and 100 pM and an increase for 5 pM, but variations of the PS amplitude were weaker than in the sham group. The role of the different CT receptor systems in this neuromodulatory effect is discussed.