Male and female Wistar rats were trained in a standard passive avoidance task. One-half of the subjects was shocked (S) upon entering a dark compartment, the other half was not (NS). One hour after S and NS experience subjects were tested. During testing different behavioral elements were observed in order to elucidate the variables which might be responsible for the observation of sex differences in passive avoidance behavior (Experiment Ia). In addition, separate groups of NS and S male and female rats were used to establish effects of sex and shock presentation on locomotor activity (Experiment Ib). One hour after S and NS experience within a passive avoidance procedure these subjects were tested for open field ambulation. Results of both experiments indicated that shock-stress reduces locomotor activity of male and female rats, but to a lesser extent in female rats. Sex differences in behavioral responses to aversive stimuli may thus be a consequence of a sex-dependent susceptability to stress-induced behavioral depression.