A survey was made of all available information about electric shock to humans, including children, at power-transmission frequencies of 50 and 60 Hz. Reliable quantitative data at these frequencies are available for three measurable physiological responses to electrical stimulation: (1) the perception of electric current flow, (2) uncontrollable muscular contraction, and (3) death. Relevant threshold conditions for response to minimum currents include the size and resistance of the body and the duration and pathway of current flow. One percent of the general populace can perceive from 0.1 to 0.5 mA of 50-60 Hz current, depending upon the type of hand contact made with an electrically-energized circuit. A safety threshold of 5 mA, recommended for the general population including children, is based upon the conclusion that any 50-60 Hz current in excess of the release threshold of an individual should be regarded as hazardous and potentially lethal. Ninety-nine percent of adult male workers should be able to release 9 mA of 50-60 Hz current. Voltages calculated from reliable experimental data on effective currents and expected resistances are lower than voltages generally recommended to be safe.