Patients with multiple myeloma had 15 times more infections a year than a control population with arteriosclerotic heart disease. The prevalence of hospital-acquired, gram-negative infections with myeloma has increased in recent years. Infections occurred five times more frequently in persons with chronic lymphocytic leukemia than among the controls; the prevalence of gram-positive infections acquired away from the hospital may be declining with this leukemia. Patients with either of these immune cell neoplasms were particularly susceptible to body surface infections with common bacterial pathogens as others have observed with primary antibody deficiency diseases. These infections caused marked morbidity and mortality. Infections appeared to occur most frequently among relatively young and geriatric patients.