Eighteen febrile patients experienced 24 episodes of Bacillus bacteremias from January 1978 to June 1986. Bacillus species isolated included Bacillus cereus (eight cases), Bacillus circulans (three), Bacillus subtilis (two), Bacillus pumilus (two), Bacillus licheniformis (one), Bacillus sphaericus (one), Bacillus coagulans (one), and six that could not be speciated. Fifteen patients had lymphoma or leukemia and three had breast cancer. Nine patients were neutropenic (polymorphonuclear neutrophil count, less than 1.0 x 10(9)/L), seven patients had a Hickman catheter in place, and 14 had recently received chemotherapy. Twelve of the bacteremic episodes were clinically significant, and four of these 12 involved Hickman catheters. Catheter removal was ultimately necessary in all four patients. Scanning and transmission electron microscopy was performed on one of the removed Hickman catheters and showed Bacillus organisms embedded in a biofilm composed of gram-positive cocci and glycocalyx. Bacillus species were uniformly susceptible to vancomycin, imipenem, and aminoglycosides, with penicillin susceptibilities being variable. Bacillus appears to be another gram-positive organism now being recognized as a bacterial pathogen for compromised hosts. When such infections involve long-term indwelling venous access devices, treatment should include immediate catheter removal as well as antibiotic therapy.