Homosexually active men have frequent intestinal and rectal symptoms resulting from sexually acquired gastrointestinal infections. We evaluated the histologic findings in rectal biopsy specimens obtained from 89 homosexual men with intestinal symptoms and 11 homosexual men without intestinal symptoms. All had undergone comprehensive microbiologic evaluation for rectal and enteric pathogens. Rectal biopsy specimens were evaluated without knowledge of clinical or microbiologic data by a standardized method for the presence or absence of abnormal histologic features. Forty-six percent of specimens from symptomatic men and 27% of those from asymptomatic men were abnormal. Acute inflammation was the most frequent histologic abnormality and was more frequent in men who had pathogens (51%) than men without pathogens (24%, p less than 0.02). Acute but not chronic inflammation was seen also in specimens from homosexual men without intestinal symptoms. Intestinal spirochetosis was present in specimens from 23 (26%) of the symptomatic and 5 (45%) of the asymptomatic men. In 5 of the 89 symptomatic men, biopsy features of idiopathic inflammatory bowel disease (IIBD) were present; all 5 of these men were infected with either Treponema pallidum or Chlamydia trachomatis. Features of IIBD were present in 25% of those infected with C. trachomatis or T. pallidum. Chronic inflammation was more frequent in men infected with C. trachomatis, syphilis, or herpes simplex virus type II: 31% vs. 3%, p = 0.0002. Acute inflammation was present in specimens from men with proctitis or proctocolitis and enteritis as well as in those from asymptomatic men, whereas chronic inflammation was present only in specimens from men with proctitis or proctocolitis. Both acute and chronic inflammation were more frequent when biopsy specimens of the abnormal mucosa were examined. When specimens from men with single infections were analyzed, histology was rarely diagnostic. We conclude that acute inflammation is frequent in rectal biopsy specimens from symptomatic and asymptomatic homosexual men; chronic inflammation is infrequent, but when present is significantly associated with syphilis, herpes simplex virus type II, and C. trachomatis infection.