Fifty-five patients who received od gentamicin were studied. The protocol for od gentamicin was followed in 23/55 (48%). Cure rates were 22/23 (96%) when the protocol was followed and 24/32 (75%) when not followed (P = 0.06). Toxicity was more common in those in whom the protocol was not followed (9/32; 28%) than in those in whom it was followed (1/23; 4%) (P < 0.05). The number needed to treat with the protocol to produce one additional cure was 4.84 (95% CI 2.64 to 28.66) and the number needed to treat to prevent one case of toxicity was 3.61 (95% CI 2.16 to 10.99).