We delineated the dose-and time-dependent retinal toxicity of intravitreal ceftazidime using electroretinography (ERG) in phakic rabbit eyes. Toxicity was evaluated following intravitreal doses ranging from 0.5 to 50 mg/0.1 ml. Eyes were examined prior to injection, at one day, and at seven days after injection. ERG patterns at one and seven days indicated a toxic response to doses of 20 to 50 mg. Doses of 10 mg or less gave a transient depression of the B-wave at one day, but a return to normal was observed at the seven-day evaluation. Pharmacokinetic analysis following intravitreal injection of 2 mg of ceftazidime into uninfected phakic rabbit eyes disclosed vitreous levels of: 1711 micrograms/ml at 0 hr; 1340 micrograms/ml at 8 hr; 451 micrograms/ml at 24 hr; 270 micrograms/ml at 48 hr and 67 micrograms/ml at 72 hr. Peak aqueous humor level was 139 micrograms/ml 8 hr post-injection. Potentially therapeutic drug levels were obtained in the aqueous and vitreous humors following a nontoxic intravitreal dose of ceftazidime in a rabbit model.