Simian acquired immunodeficiency syndrome (SAIDS) is a retrovirus-induced immunodeficiency disease that affects certain nonhuman primates and has many parallels to human AIDS. We examined 72 rhesus monkeys (Macaca mulatta) exposed to SAIDS retrovirus serotype-1 (SRV-1) and 81 healthy control monkeys at the California Primate Research Center to determine the prevalence of oral lesions. At the time of examination, 69 of the 72 monkeys exposed to SRV-1 had serologic and/or virologic evidence of SRV-1 infection. None of the 81 control monkeys had any evidence of infection with SRV-1. Acute necrotizing ulcerative gingivitis (ANUG), oral yeast infections, and noma occurred in 10% (p less than 0.01), 4%, and 1%, respectively, of the study group of 72 animals but were found in none of the control animals. Thus, ANUG occurs rather frequently in rhesus monkeys with evidence of SRV-1 infection. The reproducible immunodeficiency that follows inoculation of SRV-1 in rhesus monkeys promises to be a useful model for studying the pathogenesis of ANUG associated with immunodeficiency.