Methods, whether or not acceptable in the correct killing of fish, amphibians, reptiles or birds, are reviewed. The acceptable or unacceptable character of each of these techniques is commented upon. The techniques are differentiated into mechanical, chemical and physical methods. Of all mechanical techniques, rendering an animal unconscious by a sharp blow on the head, followed by rapid decapitation is an acceptable method. Of the chemical techniques, inhalation of Halothane, CO2 + O2, or ether, are usually acceptable. Cutaneous absorption by bathing in a solution of the anaesthetic tricaine sulphonate (MS 222) is the method of choice in fish and amphibians. The injectable anaesthetics T61 and pentobarbital-Na are acceptable in all groups of animals. Physical techniques such as supercooling, heating or electrocution are either unacceptable or impracticable in veterinary practice. Attention is paid to the effects of each of these techniques on the animal, the executing individual and the owner. Technical details of the methods most preferable in the humane killing of animals are discussed.