Serious infections caused by organisms of the genus Bacillus developed in seven patients. Five drug abusers had either endocarditis or osteomyelitis, one leukemic patient had necrotizing fasciitis, and one patient had a ventriculoatrial shunt infection with recurrent bacteremia. All patients recovered. Experience with these cases reemphasizes the importance of not dismissing Bacillus organisms as culture contaminants, especially when isolated from blood, body fluids, or closed-space infections.