1. Current problems in immunotoxicology are reviewed with special attention to the sensitivity of the immune system to the effects of xenobiotics. 2. Sensitivity of target cells, route of exposure, dosage, mechanism of action and response of the immune system are discussed as the main factors responsible for the ultimate effects of drugs and chemicals. 3. The methodology of immunotoxicology is divided into two main steps: preclinical screening and the monitoring of exposed persons. 4. Conclusions are prescribed about future tasks in human immunotoxicology.