Aspirin prolongs skin bleeding time in man by inducing abnormal platelet function. Prolongation of gastric bleeding time has been postulated as a mechanism for gastric hemorrhage after aspirin in man. To determine whether endoscopic gastric biopsy is safe in patients taking aspirin, we studied the effects of acute and chronic aspirin use on gastric bleeding time in four groups of subjects. Gastric bleeding time was assessed directly following endoscopic biopsy. Skin bleeding time was done by the Mielke method. Control subjects (group I) were studied twice at one-week intervals to determine reproducibility of the gastric bleeding time technique. The effect of aspirin on gastric and skin bleeding time when given to normal volunteers for 24 hours (group II) and for two weeks (group III) and to rheumatic disease patients on a chronic basis (group IV) was also studied. In normal volunteers given aspirin for 24 hours or two weeks, gastric bleeding time was not affected in spite of skin bleeding time being significantly prolonged over baseline. Gastric bleeding time was less then skin bleeding time in all groups including patients with rheumatoid arthritis (p less than 0.05). We conclude that aspirin ingestion does not prolong gastric bleeding time in man and that gastric biopsy is not contraindicated on th basis of recent aspirin ingestion.