A prospective study was performed to establish the effects on the bleeding time and the ocular toxicity of the use of intravitreal hemocoagulase (1 NIH thrombin unit/100 ml in BSS Plus) in patients undergoing vitrectomy. Sixty patients with diabetic retinopathy, penetrating ocular injury or non-diabetic retinal vascular disorder, in whom electroretinograms were recordable, were assigned to a study of Hemocoagulase-BSS Plus versus BSS Plus. The bleeding time was measured after cutting the proliferative attachments to the underlying retina. Intravitreal hemocoagulase significantly reduced the bleeding time, and this reduction of bleeding facilitated the surgery. A washout of hemocoagulase at the completion of the vitrectomy was not carried out. Hemocoagulase in the vitreous cavity assisted in maintaining hemostasis during the first week after diabetic vitrectomy. Postoperative electroretinography data did not show any disadvantage for the hemocoagulase infusate. Clinical study showed no adverse effect on the cornea, lens or visual acuity.