The effect of blood culture results on patient management in a department of internal medicine was analyzed retrospectively. In a series of 300 patients 538 blood cultures were taken. Fifty-four (10%) of blood cultures from 44 of the 300 patients were positive, but in 16 patients cultures yielded organisms considered to be contaminants. Only 28 (9.3%) patients' cultures showed growth of clinically significant pathogenic bacteria. Antimicrobial chemotherapy was instituted in 234 (78%) patients before culture results were available. For only 21 (7%) patients did the result of the blood culture have any therapeutic consequences. The high frequency and lack of impact of negative blood cultures demands a more appropriate protocol for blood culturing, and guidelines are suggested.