In the forgoing papers, the authors have reported the relation between vitamin D and active sulfate metabolism (1-4), and the isolation of vitamin D sulfate from mammalian milk (5). Further tests for the antirachitic potency of human milk (containing 780I.U. of total vitamin D in 2ml as determined by the authors) by prophyrachitic and curative methods using rats previously fed on a vitamin D -defficient diet showed the positive results both in X-ray and AOAC ash test .