The interstrain differences in passive avoidance conditioning were studied in male and female KHA (Koltushi High Avoidance) and KLA (Koltushi Low Avoidance) rats. These strains were selected for the rate of acquisition of active avoidance in a shuttle box. It was shown that the passive avoidance was substantially better acquired in the KLA strain than in the KHA. In females KHA rats the capability for passive avoidance conditioning depended on the estrus phase: the conditioning was impossible in proestrus.