Profound racial differences exist in the incidence of osteoporosis, particularly in women. To investigate possible underlying reasons for this, we have measured the circulating levels of calcitonin (iCT), a bone-protecting hormone, and its flanking peptide, katacalcin (iKC), in black Gambian and white British populations. Whilst sex differences in both peptides were observed, with males having higher levels than females, the most striking finding was that white women have the lowest iCT levels. This important observation may explain, at least in part, why osteoporosis is particularly a disease of white, postmenopausal women.