Adult male Wistar rats were bilaterally implanted with indwelling cannulae in the hippocampus. Forty-eight hours after surgery, animals were habituated to an open-field box during 2 min, being tested 24 h later; next they were trained in a step-down inhibitory avoidance task (3.0 s, 0.4 mA foot-shock), being tested again 24 h later. Immediately after the training session of each task, animals received a 0.5-microl infusion of calcium-phosphate-buffered saline (PBS) and S100B (20, 200, 2000, or 20,000 nM). In the inhibitory avoidance task, animals infused with the two highest concentrations of S100B, 2 and 20 microM, obtained higher scores of retention relative to controls in the test session (p<0.05), and a trend toward an increase was observed in animals infused with 200 nM (p<0. 10). In both sessions of the habituation task, groups were not different regarding crossings, rearings, and time for leaving the first square (p>0.10). These results indicate that, in rats, post-training increased hippocampal levels of S100B right after training facilitate, in a dose-dependent way, long-term memory for an inhibitory avoidance task, but not for an open-field habituation.