Hemorrhage during vitrectomy for diabetic retinopathy or in the recently traumatized eye can complicate the surgical procedures and might cause termination and failure of vitrectomy in some cases. The effect of the hemocoagulase, Botropase, on the hemostasis of intraocular bleeding was evaluated in a rabbit model by cutting central retinal vessels in the medullary ray. Addition of the hemocoagulase (1 NIH unit/100 ml) to BSS Plus significantly reduced bleeding time. Immediately after vitrectomy with the use of this hemocoagulase, the average of the maximum amplitudes of the b-wave in electroretinography was normal, although the sensitivity of the electroretinogram was reduced by 0.1 log unit in the experimental eyes which were infused with hemocoagulase solution. The sensitivity showed no significant difference after the second postoperative day. The experimental eyes showed no abnormal findings histologically. Infusate containing Botropase appeared to be a useful adjunct for the control of intraocular bleeding during vitreous surgery.