A total of 399 patients with multiple myeloma and an equal number of match controls were interviewed about factors possibly related to the causes of their disease. Factors studied included occupation, chemical exposure, radiation exposure, prior diseases, immunizations, chronic infections and markers for defects in immune regulation. A strong risk associated with agriculture/food processing was observed (RR = 1.8, P = 0.002). The risk could not be restricted to those exposed to animals or meat products, or those exposed to pesticides. Significant excesses were also noted for reported exposures to chemicals and gases/fumes, but no specific agent or group of agents could be identified. Cases had fewer tonsillectomies above the age of 10 (P = 0.01). A large excess of shingles (herpes zoster) was observed in cases (P less than 0.001), but most of the excess cases occurred within 10 years of diagnosis, suggesting this was a preclinical manifestation of disease rather than a cause of it.