he established that the skin was not only the organ responsible for making vitamin d3 but was also a target tissue for its active form, 1,25-dihydroxyvitamin d3. he determined the extremely inhibitory effects of 1,25-dihydroxyvitamin d3 on keratinocyte proliferation and the promoting effects on differentiation, and translated these seminal observations by demonstrating that the topical application of 1,25-dihydroxyvitamin d3 and several of its analogs were effective for the treatment of psoriasis.