The influence of age, sex and body size on the bone mineral content of the radius (BMC) measured by single-photon absorptiometry has been studied in 134 British and 243 rural Gambian children aged 0-36 months. Growth rates and childhood nutrition, including calcium intakes, were markedly different in the two communities. In both groups BMC increased with age and was higher in boys (8%, P less than 0.001). Adjustment for body size (height, weight, bone width), using multiple regression analysis, removed the age effect and reduced the sex difference to 4% (P less than 0.01). Gambian children had significantly lower BMCs than British children of the same age (P less than 0.001), averaging 11% close to birth and diverging to a calculated difference of 31% at 36 months. The differential was reduced after adjustment for body size but remained significant (P less than 0.01) with BMC values diverging from birth to a predicted difference of 12% at 15 kg body weight. The extent to which these results reflect the low calcium intakes of Gambian children requires further study.