Three analogs of 1 alpha,25-(OH)2D3 with an oxygen or another heteroatom at position 23 were synthesized in search of separating the cell-differentiating from the calcemic effects of the vitamin D hormone. Their ability to induce superoxide production in human myeloid leukemia cells (HL-60) was 1 alpha,25-(OH)2D3 > 23-oxa-24-oxo-1 alpha,25-(OH)2D3 > 23-thia-1 alpha,25-(OH)2D3 > 23-oxa-1 alpha, 25-(OH)2D3. 23-oxa-24-oxo-1 alpha, 25(OH)2D3 was slightly more potent than 1 alpha,25-(OH)2D3 in inhibiting cell proliferation in MCF-7 cells and 23-thia- and 23-oxa-1 alpha,25(OH)2D3 were less potent. Their in vitro potency to produce osteocalcin in MG-63 cells was 1 alpha,25-(OH)2D3 > 23-oxa-24-oxo-1 alpha,25-(OH)2D3 > 23-thia-1 alpha,25-(OH)2D3 = 23-oxa-1 alpha,25-(OH)2D3. All three analogs had reduced receptor and DBP affinity compared to 1 alpha,25-(OH)2D3. When these analogs were injected in rachitic chicks, only little calcemic effects were observed. The introduction of a heteroatom in carbon 23 of 1 alpha,25-(OH)2D3 thus creates analogs with dissociated action on cell differentiation and calcium homeostasis.