This study examines the effectiveness of prophylactic ciprofloxacin and rifampin following high-dose chemotherapy and autologous stem cell rescue (HDC/ ASCR). Specific endpoints included the incidence of fever, clinically documented infection, bacteremia, and readmission rates from an outpatient bone marrow transplant setting following infection or fever. A group of 97 patients receiving 134 cycles of HDC/ASCR were studied. Patients were given ciprofloxacin 750 mg p.o. twice daily and rifampin 300 mg p.o. twice daily beginning on the day of stem cell reinfusion (24-48 h after completion of high-dose chemotherapy). Most patients were either discharged to an outpatient setting following completion of their chemotherapy or received all of their chemotherapy in an outpatient setting. Febrile neutropenia was treated with empirical antibiotics in an outpatient setting unless it was complicated by hypotension, renal failure, severe mucositis or other problems. The median duration of neutropenia (absolute neutrophil count below 500/mm3) was 7 days. Neutropenic fever occurred in 62% of patients but clinically documented bacterial infection occurred in only 2 (1.5%) patients during their neutropenic period. No bacteremia was noted. Readmission to the hospital following fever or infection occurred in 26% of patients maintained in the outpatient setting. There were no deaths from a bacterial infection in this study although 1 patient (0.7%) died from aspergillosis. Prophylactic ciprofloxacin and rifampin is a well-tolerated and highly effective combination that effectively decreases the risk of both gram-positive and gram-negative bacterial infection following HDC/ASCR. It facilitates outpatient management of myelosuppressed patients receiving autologous stem cell rescue.