Complement depletion in the hamster by cobra venom factor (CoF) gives a higher frequency and severity of lesions after intrahepatic inoculation of Entamoeba histolytica. The CoF-treatment does not alter the humoral immune response to amebae, indicating that its effect on the amebic liver abscess is not due to suppression of the immune response but rather to its effect on complement levels at the time of the protozoal infection.