Intraoperative circulatory collapse developed in a 56 year old man undergoing surgery after the rapid administration of five per cent plasma protein fractions (Plasmanate). The reaction was characterized by profound hypotension, peripheral vasodilation, facial edema, and pulmonary wheezes. The patient responded to administration of intravenous fluid, oxygen, atropine, ephedrine, and steroids. The cause of hypotension is not definitely established, but appears to be due to activation of the patient's kinin system. When rapidly infused, PPF may cause the production of bradykinin, a potent vasodilator. Physicians must be aware that paradoxical hypotension may occur with administration of five per cent plasma protein fractions and should use albumin solutions or other plasma expanders when rapid restoration of intravascular volume is required.