Rhizobium radiobacter is an aerobic, gram-negative bacterium closely related to several species of plant pathogens that occur in soils worldwide. It has been associated with human systemic diseases, including peritonitis, urinary tract infection, cellulitis, and myositis. Only eight isolates of R. radiobacter have been encountered in the Clinical Microbiology Laboratory at the University of Alabama at Birmingham Medical Center between 1995 and 2000, four of which were detected in blood cultures of immunosuppressed and/or debilitated patients. Both the RapID NF Plus. and the BBL Crystal bacterial identification systems readily identified the organisms. Antimicrobial susceptibilities for R. radiobacter varied and should be tested in each case to guide therapy. Drugs such as ciprofloxacin, piperacillin-tazobactam, trimethoprim-sulfamethoxazole, ceftriaxone, imipenem, gentamicin, and amikacin were reasonable therapeutic choices for the organisms we encountered.