Relatively few investigations of anaerobic bacteria as ocular flora have been conducted, and their results have been contradictory. The conjunctival sacs of 22 normal subjects and of 14 patients with acquired immunodeficiency syndrome, and 22 anophthalmic sockets were cultured for anaerobic bacteria Thirty-four (77.3%) of the 44 eyes of normal subjects harbored anaerobic bacteria; Propionibacterium acnes was present in 28 eyes (63.6%), Lactobacillus species in 6 eyes (13.6%), and Veillonella species in 7 eyes (15.9%). The finding were very similar for anophthalmic sockets (p = 0.01), with 17 (77.3%) of the 22 sockets harboring anaerobes; Propionibacterium acnes was the organism identified in 16 (72.7%) of these sockets; Veillonella was identified in 4 (18.1%), Peptococcus niger in 3 (13.6%) and P. granulosum in 2 (9.0%) of these sockets. Acquired immunodeficiency syndrome patients had the highest incidence of anaerobic organisms, with positive cultures obtained from 24 (85.7%) of the 28 eyes. Propionibacterium species were isolated from 16 (57.1%) of these eyes. Clostridium species from 10 (35.7%) eyes and Actinomyces species from 8 (28.6%) eyes. It thus appears that anaerobic organisms are common flora in normal conjunctival sacs and in anophthalmic sockets, as well as in the sacs of acquired immunodeficiency syndrome patients, but the latter group had a higher incidence (x2 = 0.87) and a spectrum of organisms that was different from that of the other two groups.