This article distills from available data descriptions of typical human symptoms in reaction to prompt total-body ionizing radiation in the dose range 0.5 to 30 Gy midline body tissue. The symptoms are correlated with dose and time over the acute postexposure period of 6 wk. The purpose is to provide a symptomatology basis for assessing early functional impairment of individuals who may be involved in civil defense, emergency medical care and various military activities in the event of a nuclear attack. The dose range is divided into eight subranges associated with important pathophysiological events. For each subrange, signs and symptoms are designated including estimates of symptom onset, severity, duration and incidence.