Plasma-11-hydroxycorticosteroid (11-OHc.s.) and growth-hormone (G.H.) levels have been measured in a party of nine young men on a week's climbing course. The results are compared with those obtained in their instructor, eleven other men after a day on the hills, and four men and one woman rescued in a state of exhaustion. Plasma-11-OHc.s. levels were increased on days of considerable physical exertion. In two of the five exhausted climbers unexpectedly low concentrations of plasma-11-OHc.s. were found. It is suggested that in patients found in a state of collapse by mountain-rescue teams, emergency administration of parenteral steroids might be beneficial.