In a prospective analysis of 4234 significant isolates from 62,437 consecutive sets of blood cultures over an 8 year period, 79.4% were detected within 48 h. Routine examination of Gram-film smears made within 24 h of receipt of the cultures detected about half of all positive cultures. Many organisms were detected earlier on Castaneda slopes than in tryptone soya broth. Haemophilus influenzae (type b) and Neisseria spp. were usually suspected on clinical grounds, and early blind subculture was successful in 95.7% and 69% of cases respectively. Resistance to trimethoprim among Gram-negative coliforms increased significantly over the 8 year period. Production of beta-lactamase was detected in 12% of Haemophilus influenzae (type b). Unlike Staphylococcus aureus, Staphylococcus epidermidis was commonly resistant to methicillin, erythromycin, fusidic acid and gentamicin.