Dr. Murray Favus is investigating the hormonal and ionic influences that regulate biosynthesis of 1,25-vitamin D3 by renal proximal tubules. Another line of investigation explores the mechanism of intestinal calcium hyperabsorption in genetically hypercalciuric stone forming rats. Studies now focus on the role of the vitamin D receptor gene and its regulation in the hypercalciuric rat. Recently, vitamin Ds role in the immune system has been elucidated. Vitamin D receptors are found on T cells and macrophages, and 1,25-D3 may be a useful treatment for autoimmune diseases such as type I diabetes.