In a double-masked, randomised, controlled study the effectiveness and safety of 0.3% ofloxacin solution were compared with those of 0.3% gentamicin ophthalmic solution in treating external bacterial ocular infections. The clinical improvement rate for patients treated with ofloxacin was 98% (51/52) and 92% (48/52) for those treated with gentamicin. Microbiological improvement was achieved in 78% (40/51) of the ofloxacin patients, compared with 67% (35/52) of the gentamicin group. Ofloxacin treatment eradicated or controlled 85% (86/101) of the Gram positive and 89% (17/19) of the Gram negative organisms cultured, compared with 83% (103/124) and 78% (29/37), respectively, after gentamicin treatment. None of these differences were statistically significant. The incidence of adverse effects attributable to ofloxacin treatment (3.2%) was less than that reported for gentamicin (7.1%). Ofloxacin proved to be an effective, safe, and comfortable therapy for external bacterial ocular infection.