During a 28-month period, endoscopic mucosal biopsy specimens from all HIV-infected patients were submitted for routine histologic evaluation. Immunoperoxidase staining for cytomegalovirus and herpesvirus antigens (esophagus), mycobacterial and fungal staining, and Gram staining of mucosal biopsy specimens were done. Special fungal and acid-fast stains were selectively performed in patients with absolute CD4 cell counts of less than 200 cells per microliter (200 x 10(6)/L) and/or with diarrhea and or wasting syndrome. Treatment was based on the endoscopic and histologic findings, and long-term follow-up was performed. The 121 symptomatic HIV-infected patients underwent 221 upper and/or lower endoscopies with 285 biopsy sites. The sensitivity and specificity of H&E staining for the diagnosis of gastrointestinal cytomegalovirus were 97% and 100%, respectively. The results of fungal and mycobacterial stains neither altered therapy nor identified previously undiagnosed infections in any patient. Long-term follow-up revealed no patient in whom an infection was missed on routine H&E, which affected outcome. Routine H&E staining is accurate for the diagnosis of gastrointestinal opportunistic infections in HIV-infected patients. Special histologic stains for fungal, mycobacterial, and viral infections did not increase the diagnostic yield or alter medical therapy but doubled the costs.