A hospital-based case-control study of 153 multiple myeloma (MM) cases and 459 controls was conducted to evaluate the hypothesis that chronic or frequent infections or allergic and autoimmune diseases might be of higher prevalence in individuals who develop MM. Information was obtained by direct interviews of subjects. Controls were matched to cases on age, sex, race, and hospital. "Immune-stimulating conditions" included chronic infections such as pyelonephritis, urinary tract infections (UTIs), prostatitis, rheumatoid arthritis and other collagen vascular diseases, allergies, bronchitis, tuberculosis, cholecystitis, diverticulitis, and osteomyelitis. The overall odds ratio (OR) (odds of history of immune-stimulating conditions in cases versus controls) was 0.4 (95% confidence interval = 0.3-0.7) which suggested that cases had significantly less immune-stimulating conditions than did controls. The exposure rate for these conditions was high for cases (0.7) as well as for all control groups (0.8). These findings suggest that immune-stimulating conditions alone are not the causative factor in the etiology of MM, though they may play a role in the predisposed individual.