AbstractWith the evident increase in osteolytic disease, especially in black-skinned urban communities, it has become necessary to attempt to define and measure dietetic and environmental factors contributing to this increase. This paper describes and measures calcium absorption and excretion and serum hydroxy-cholecalciferol (Vit D3) levels in both black-skinned and caucasian controls exposed to similar doses of ultra-violet light. It is concluded that there is a significant difference in response to UVL stimulus between the two groups to the detriment of the blackskinned population.