We performed a prospective study involving 96 patients undergoing vitrectomy for proliferative diabetic retinopathy to determine the effect of epsilon-aminocaproic acid on the occurrence of postoperative intraocular hemorrhage. epsilon-Aminocaproic acid significantly reduced postoperative vitreous hemorrhage during the immediate postoperative period. Follow-up examinations two to six weeks after discharge from the hospital disclosed no statistically significant difference in the severity of vitreous hemorrhage between the treated and untreated groups. The loss of drug effect at this stage was in part due to spontaneous repeated bleeding in the treated group and in part to spontaneous clearing of hemorrhage in the untreated group. There was no statistically significant difference in the rate of repeated bleeding between the two groups or in rate of spontaneous clearing.