In order to assess the effect of nutrition on bone mass, radiographs were taken of animals subject to seasonal stress on Hirta, Hebrides, and of Soays from well-nurtured herds at Babraham and Aberdeen. The ewes from Hirta had significantly lower values for combined cortical thickness (CCT) than those from the unstressed herds, whereas the Hirta rams showed no significant reduction in CCT. It appears that there is a difference of bone metabolism because of the additional stress of gestation and lactation suffered by ewes enduring a seasonally restricted food supply.