Eleven Human Immunodeficiency Virus 1 (HIV1)-infected patients (10 male, 1 female; age 23-51 years (median 36); 10 male homosexuals, 1 IV drug abuser; WR3 1 patient, WR5 5, WR6 5) with intestinal Cytomegalovirus (CMV)-manifestations were compared with a group of 78 HIV1-infected patients in respect to their clinical, immunological and virus-serological data and the results of the histological and microbiological examination of endoscopically obtained biopsies. No differences were observed on age, sex, risk of infection, stage and immunological status. Bloody diarrhea was most important in discriminating CMV-colitis and non-CMV-related intestinal manifestations. Dysphagia and other symptoms occurring in patients with CMV-esophagitis were not able to predict CMV-esophagitis specifically. 6 of 11 patients with serological findings consistent with an active CMV-infection had no detectable CMV-manifestations; 6 of 11 patients with intestinal CMV-manifestations did not show serological findings suggestive of active CMV-infection. Ulcerative alternations of intestinal mucosa represent the most powerful indicator of intestinal CMV-disease in endoscopical examination. Only in two patients, ulcerative alterations were seen without diagnosis of CMV-disease being established. CMV was isolated in one of 11 patients, in two patients CMV was isolated from biopsies of unchanged mucosa. Simultaneous infection by HSV and CMV was detected in three patients, in one patient in the same localisation. Histology revealed inclusion bodies in 8 of 11 patients with intestinal CMV-disease, in no case inclusion bodies were seen without CMV-disease.