Immunosuppression, possibly in combination with viruses, could be a main etiologic mechanism for non-Hodgkin's lymphoma (NHL). Chemicals such as phenoxyacetic acids, chlorophenols, dioxins, organic solvents, polychlorinated biphenyls, chlordane, and immunosuppressive drugs have been associated with this disease. Also UV light and blood transfusion have been postulated to be risk factors. Conclusive evidence of a causal association with NHL is not established for all of these exposures, but experimental evidence and clinical observations indicate that all these exposures have in common that they may impair the immune system. Furthermore, acquired and congenital immune deficiency as well as autoimmune disorders increase the risk for NHL. In view of currently available evidence, the first priority for reducing morbidity due to NHL might be to take action against adverse chemical exposures as a measure that is more easily achievable than any other kind of prevention.