Background and Aims: To evaluate the role of tumor necrosis factor a (TNF-α), a key inflammatory cytokine, in cytomegalovirus-associated gastrointestinal disease, we quantitated the level of TNF-α messenger RNA (mRNA) in esophageal mucosa from patients with cytomegalovirus-associated esophagitis and acquired immunodeficiency syndrome. Methods: Four patients underwent endoscopic biopsy of their cytomegalovirus-associated esophageal ulcers before and after ganciclovir therapy. The level of TNF-α mRNA in coded esophageal specimens was assessed by in situ hybridization, reverse- transcription polymerase chain reaction, and quantitative polymerase chain reaction. Results: Esophageal mucosa from 3 patients whose ulcers healed or markedly improved contained before therapy numerous macrophages expressing TNF-α mRNA and high tissue levels of TNF-α mRNA that decreased substantially or were not detectable after therapy. In contrast, esophageal specimens from the single patient whose ulcer worsened after therapy contained many mucosal macrophages expressing TNF-α mRNA before as well as after therapy, and the high number of molecules of TNF-α mRNA present in the tissue before therapy increased further after treatment. Conclusions: Increased macrophage production and high tissue levels of TNF-α mRNA are associated with cytomegalovirus-associated esophageal ulcers and probably contribute to the inflammatory response associated with cytomegalovirus- induced gastrointestinal disease.