NMRI mice of both sexes and in various stages of the suckling period were handled oncea day for three minutes. They were intraperitoneally infected with E. coli O 111 on the eighteenth day of life. Handling carried out from the first to the 18th day led to a significantly higher mortality (P = 1,4%) as compared to the control animals. Differences in mortality were not observed when the stimulation occurred on the 1st to 10th or 10th to 18th day of life. Weight determination carried out just prior to infection showed no remarkable differences between the experimental groups.