Carrot (Daucus carota) cell cultures were found to secrete a protein, with the molecular weight of 58,000, which could strongly enhance the activation of carrot prophenoloxidase by CaCl(2). The protein was isolated from the culture filtrate and purified to electrophoretic homogeneity. The purified protein did also show hemagglutinating activity toward rat as well as rabbit erythrocytes and this activity was inhibitied by N-acetylglucosamine or fetuin.