The medical records of 52 patients (53 eyes) with culture-proven gram-negative endophthalmitis between January 1982 and December 1990 were reviewed. Pseudomonas aeruginosa (23% [12/53]) and Haemophilus influenzae (19% [10/53]) were the most frequent isolates in this series. Overall, 26 (49%) of 53 treated patients achieved 20/400 or better visual acuity. Fifty-two (98%) of the original 53 gram-negative isolates were sensitive to the aminoglycoside antibiotics. To determine their sensitivity to recently developed antibiotics, 35 of the isolates were again grown on culture media and their sensitivities to ceftazidime, ciprofloxacin, and imipenem were obtained. Only ceftazidime demonstrated in vitro efficacy for all the organisms tested.