Vitamin D (Vitamin D) deficiency is very common. We recently showed that 97% of 204 patients admitted to Truman Medical Center were Vitamin D deficient (<30 ng/ml). However, the consequences of Vitamin D deficiency, particularly with respect to infection, are not well understood. It is known that production of cathelicidin, an important antimicrobial peptide, is critically dependent upon Vitamin D. It is also established that levels of cathelicidin correlate inversely with urinary tract infection risk. We hypothesize that restoration of Vitamin D levels to normal in patients undergoing major surgery will result in significant decreases in levels of perioperative infections due to restoration of normal levels of circulating Vitamin D, which in turn will elevate cathelicidin levels. As an initial test of this hypothesis, we propose a double-blind, prospective, randomized study of pre-operative Vitamin D supplementation. Fifty subjects undergoing surgery will receive daily Vitamin D3 (50,000 IU) for five days pre-operatively, with controls receiving placebo. Levels of Vitamin D, calcium, cathelicidin, and the pro-inflammatory protein resistin, will be monitored before Vitamin D supplementation (pre-operatively) and after Vitamin D supplementation (post-operative days 1 and 2). The effect of these changes should be to decrease the incidence of infectious complications. We expect to observe Vitamin D levels increase to normal, and cathelicidin levels become elevated. We expect to see increased levels of resistin in patients developing infections. This study will provide strong pilot evidence for future NIH funding.