&NA;Histologic and ultrastructural examination of specimens of rectal mucosa from 11 patients who had recently consumed excessive quantities of alcohol revealed marked pathologic changes. Goblet cells were decreased and a dense mononuclear cell infiltrate was seen on light microscopic study. Electron microscopy revealed swollen, distorted mitochondria and dilated and vesicular endoplasmic reticulum. These abnormalities disappeared after two weeks' abstinence. It is suggested that disordered organelle structure and function might contribute to the diarrhea frequently observed following excessive alcohol intake.