Immunologic effects of a new pharmaceutical molecule are often studied by in vitro immune assays and in laboratory animal models. However, immunologic activity can also be evaluated in man during the early clinical stage of drug development. Measures of immunologic response have recently served as surrogate clinical endpoints for drug approval. A variety of non-invasive measures can determine if a test molecule enhances or suppresses immunity. Both antibody and cellular immune responses to a new molecule itself can be detected and quantified in man. Assuring the successful outcome of a clinical trial incorporating immunologic parameters however, requires a realistic approach to protocol development, care in site selection, and a critical evaluation of participating laboratories. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.