There are many ways in which immunotherapeutic agents could potentially cause developmental toxicity. According to the published data in humans and animals, however, this class of drugs does not appear to present any increased risk of reproductive toxicity by comparison with other therapeutic classes. The basic testing strategy outlined in the ICH guidelines is suitable for the preclinical reproductive toxicity assessment of these drugs (except vaccines). Particular consideration needs to be given to the choice of species when testing antibodies or human molecules. Immune-active drugs may have the potential to interfere with the development of the immune system. For this reason, it may be advisable to assess the integrity of the immune system in animals previously exposed to the test substance during development. Such tests can easily be appended to the study design of the pre- and post-natal study. In view of the lack of any provision for post-weaning exposure in the guidelines and the late maturation of the immune system, a separate post-natal study may be considered for drugs that are likely to be prescribed to children.