Abstract Problems with conventional water bath stunners have been identified through observation in commercial processing plants and experiment in the laboratory. Due to differences in the electrical resistance of the individual birds there is little control over the stunning current and hence the effectiveness of stunning. To illustrate this problem, the use of set voltage waterbath stunners in the poultry processing industry is described. Their performance in relation to existing UK legislation and proposed European standards for animal welfare is discussed. A prototype poultry stunner has been developed which controls the current delivered to individual birds. The stunning current has a 50 Hz sinusoidal wave form and the root mean square (r.m.s.) value is adjustable between 50 and 200 mA. The machine is capable of operating at typical commercial processing speeds of 6000 birds per hour. Experiments using dummy birds, built with electrical properties to represent a live chicken, show that the system can deliver and maintain a preset, constant current to each individual bird provided there is no significant current pathway between adjacent birds. A constant current stunning system will control the current flow through individual birds at an optimal level which will ensure an effective stun and at the same time minimize the carcass quality problems produced by high currents.