1 alpha,25-Dihydroxyvitamin D-3 (1,25-(OH)(2)D-3) the biologically active form of vitamin D-3, not only plays a major role in mammalian calcium and phosphorous homeostasis but also exerts pleiotropic effects on cell proliferation, differentiation and the immune system. Further, vitamin D is believed to play a significant role in the prevention of colon, prostate, and breast cancer and in reducing the risk of autoimmune diseases. To gain insight into the mechanism whereby vitamin D can have such diverse actions, we have employed microarray technology. We studied the effect of a single dose of 1,25-(OH)(2)D-3 on gene expression in the intestine of vitamin D-deficient rats. Within 6 h, 1,25-(OH)(2)D-3 stimulates the expression of several phase I and phase II biotransformation genes. There is also an increased expression of antioxidant genes. These results support the idea that vitamin D is a significant factor in detoxification and protection against environmental toxins. (c) 2006 Elsevier Inc. All rights reserved.