To facilitate the early diagnosis of exogenous fungal endophthalmitis, we developed a rabbit model for Aspergillus fumigatus endophthalmitis. Six eyes of six New Zealand white rabbits were inoculated with forty spores of A. fumigatus. A control group of their six contralateral eyes received a similar but sterile inoculum. The rabbit eyes were evaluated with respect to clinical appearance and the electroretinogram. Clinically evident endophthalmitis developed in all six infected eyes at an average of five days after injection (range 3-7 days). Data samples each 48 hours showed transient b-wave amplitude elevations in three infected eyes. These were greater than two standard deviations above the mean pre-injection values (p less than 0.05). These amplitude increases preceded the onset of ophthalmoscopically recognizable infection and were observed at 2 to 5 days after injection (mean = 4 days). B-wave amplitudes in the infected eyes fell below two standard deviations of pre-injection values (p less than 0.05) at an average of 5 days (range 3-7 days) after injection, a corresponding to the onset of clinically obvious infection. At an average of 7 days after injection, all the infected eyes exhibited unmeasurable electroretinogram waveforms and severe infection. Histopathologic study of infected eyes showed extensive fungal infiltration of retina and vitreous tissues. The electroretinogram may be helpful in the early diagnosis of fungal endophthalmitis.