A protein has been isolated and partially purified from the venom ofNaja naja which causes the noncytolytic release of amines from rat peritoneal mast cells. This protein, termed CVA protein, has been demonstrated to have a molecular weight of 18,500 and sedimentation coefficient of approximately 2s. The activity of CVA protein is destroyed by treatment for 5 min at 100°C, but is not affected at 75°C for 30 min. The ability of CVA protein to initiate mast-cell degranulation has been demonstrated to require both cell energy and calcium. The temperature sensitivity and the cellular requirements distinguish the CVA protein from phospholipase A.