A number of investigations have suggested that cadmium may exert immunosuppressive effects in animals even though conflicting findings, due mainly to varying conditions of exposure, have been reported. Overall, cadmium has been shown to enhance humoral immune responses at low levels of exposure, whereas higher ones may result in either no effect or decreased antibody production. By contrast, cell-mediated immunity was more consistently shown to be depressed. Similarly, phagocytosis, natural killer cell activity and host resistance toward experimental infections were markedly impaired in most instances. Very few data are available regarding cadmium immunotoxicity in humans. Hypersensitivity reactions have so far not been described. No immune alterations were found to be associated with "chronic cadmium disease", whereas a depressed phagocytosis, the clinical relevance of which remains to be established, was recently documented in cadmium-exposed workers. Further investigations are therefore needed to determine how immunotoxic cadmium actually is and what health consequences are to be expected in occupationally or environmentally exposed humans.