A method was developed to determine vitamin Da in milk. It includes saponification, solid phase extraction and HPLC. Recovery of added vitamin Da was 93%. Vitamin Da concentrations in commercial milks were variable. Stability studies showed that on exposure to light, there was a slight loss of vitamin Da from fortified milk. Air exposure did not affect stability in milk. Upon standing there was some stratification of the vitamin in milk containers with slightly more vitamin Da in the top layer of milk than at the bottom.