Uremic patients are known to be particularly susceptible to infections and possibly cancer. They have a definite cutaneous anergy to the various antigens used to test delayed-type hypersensitivity. However, in vitro investigations of the individual functions involved in the immune response have not disclosed a profound and reproducible defect of one of these functions. This could be due to the heterogeneity of the patients studied (uremia of differing etiology, variation in metabolic and nutritional conditions, and influence of multiple complications). It is also possible that the main defect lies in regulation and cooperation between the individual functions.