Felypressin (PLV-2), a synthetic derivative of vasopressin, a potent vasoconstrictor which has little or no effect on cardiac rhythm when given in the presence of anesthetic agents such as cyclopropane or halothane. In 25 patients undergoing craniotomy procedures under general anesthesia, the scalp was infiltrated along the projected line of incision, with a solution of either felypressin (5 international units/10 ml), epinephrine (1:100,000 solution), or physiological saline. The blood loss was determined gravimetrically and expressed in gm/cm of incision. The study was carried out in a double blind manner, with coded ampuls in a random sequence of drugs. Felypressin and epinephrine were equally effective in reducing the blood loss to approximately one third of the amount lost with saline. The difference from saline was statistically significant for both epinephrine and felypressin.