1. Enzymatic formation in vitro of vitamin D2 sulfate by various animal tissues was studied and the biosynthesis of the sulfate was proved by using the rat-liver homogenate. 2. Chemical synthesis of ammonium vitamin D2 sulfate was performed and some physicochemical properties were reported. 3. Vitamin D3 sulfate was also isolated from rabbit urine after oral administration of vitamin D3. It was in agreement with the synthesized sample.