To evaluate the usefulness of blood cultures in patients admitted with pyelonephritis, a retrospective chart review was-conducted of inpatients at a 594-bed urban, academic medical center from 1990 through 1992 with a primary discharge diagnosis of pyelonephritis. A total of 338 patients had this primary discharge diagnosis. One or more sets of blood cultures were obtained in 307 patients (91%). Fifty-six (18%) patients had a positive blood culture; 24 (32%) positive blood cultures grew coagulase-negative Staphylococcus species, in all but two instances considered a skin contaminant. Of the blood cultures drawn, only 1 (0.2%) grew a pathogenic organism not found in the urine culture, with no impact on clinical management. These results support the conclusion that blood cultures are rarely clinically useful and seldom vary from urine culture results. Potential annual cost savings of between $10 million and $20 million in the United States could result from eliminating routine blood cultures in the setting of uncomplicated acute pyelonephritis.