We analyzed 1,010 consecutive penetrating keratoplasties to determine the incidence of postoperative endophthalmitis, the frequency of positive donor rim cultures, and whether a correlation between these two factors exists. There were three cases of bacterial endophthalmitis, all caused by streptococci, and one case of Candida albicans endophthalmitis. In all cases except one case of streptococcal endophthalmitis, the same organism was cultured from the donor rim. We cultured 138 organisms from 128 of 932 donor rims (14%). A remarkable percentage of gram-positive organisms were resistant to gentamicin, the only antibiotic contained in corneal storage media. On the basis of our data and previously published data, we believe that donor material is frequently the source of microorganisms in endophthalmitis after penetrating keratoplasty.