Guidelines for antibiotic prophylaxis of infective endocarditis prior to fibreoptic bronchoscopy, are based on only five studies, which showed a bacteraemia rate of <1% among 291 patients studied. T his study was designed to expand the current data regarding the frequency of bacteraemia following fibreoptic bronchoscopy. Aerobic and anaerobic cultures of venous blood and of lavage fluid were drawn from 200 consecutive patients undergoing fibreoptic bronchoscopy without respiratory infection or antibiotic treatment prior to the procedure. The true bacteraemia rate was calculated after excluding probable "contaminated" blood cultures. A possible correlation between type of procedure performed during the bronchoscopy and occurrence of bacteraemia was investigated. Positive blood cultures were noted following 26 bronchoscopy examinations. Coagulase negative Staphylococcus was found in the cultures of 18 patients, coagulase positive Staphylococcus in 3 patients, nonhaemolytic streptococci and a Klebsiella species in 2 patients each, and beta haemolytic streptococcus in one patient. After exclusion of 13 "contaminated" specimens the bacteraemia rate was 6.5% (13/200 patients). This study showed a bacteraemia rate of 6.5%, significantly higher than previously recognized in a cohort of patients undergoing fibreoptic bronchoscopy without either pulmonary infection or an unusually high rate of invasive procedures. These findings should be taken into account in future evaluations of recommendations for antibiotic prophylaxis of endocarditis.