The efficacy of an antimicrobial regimen for prevention of infections was prospectively evaluated in 113 patients undergoing autologous bone marrow transplantation (BMT). Ciprofloxacin, 500 mg orally twice a day plus antifungal prophylaxis, fluconazole 50 mg once daily plus amphotericin B tablets or suspension and tablets, each 200 mg four times a day, was given. In addition all patients received streptococcal prophylaxis for 10 days after BMT. Documented infections occurred in 39% (44 of 113) of patients and unexplained fever in 27% (30 of 113). The efficacy of this regimen was reflected in a low mortality rate (3.5%) from infections and in the low need for intravenous amphotericin B (7%). No benefit of protective isolation was found in 59 patients compared with 54 patients treated without isolation measures.