Many medicinal products, and industrial as well as environmental chemicals have been reported to induce immune changes in laboratory animals. However, a majority of these changes were noted in conditions which were not adequately controlled and/or selected on realistic grounds as regards the route, the duration and the magnitude of exposure, so that caution should be exercised when interpreting data obtained in early non-clinical immunotoxicity studies. Nevertheless, these findings indicate that the immune system is a target organ for toxic injury so that a systematic and thorough assessment of the immunotoxic potential of xenobiotics is certainly warranted in contrast to what is suggested by the current status of immunotoxicity regulations worldwide. In addition to histological and functional immune changes, hypersensitivity reactions and to a much lesser extent autoimmune reactions have been described. Except for hypersensitivity reactions, data in humans are scarce and efforts should be paid to investigating better the immunotoxic effects of xenobiotics in man.