Circadian rhythms are 24-hour rhythms that occur in a wide range of biological functions from cellular activity and metabolism to behavior. The suprachiasmatic nucleus (SCN) is the master circadian pacemaker (or clock) influencing physiology, such as immune function, the cardiovascular system, and metabolism, as well as influencing behavior, such as activity patterns, sleep, and feeding behavior. Vasoactive intestinal peptide (VIP) coordinates these daily rhythms in the SCN by synchronizing pacemaking neurons. However, VIP has both circadian and non-circadian physiological effects. Using a strain of mutant C57B mice, transgenic with nonfunctioning VIP, and wildtype C57B mice (Mus musculus), we investigated how the disruption of the circadian rhythm affects basal metabolic rate (BMR), food intake, and immune function. We found that the VIP -/- mice had a higher BMR than wild type mice but no significant difference in immune function. Additionally, a lack of a normal light/dark circadian cycle leads to an increased average daily food intake in the mice. Currently, we are further investigating the nature of these differences, and how much of these differences may be due to the non-circadian effects of VIP. This includes: 1) measuring daily food intake to assess feeding behavior and energy intake; 2) measuring oxygen consumption of mice through respirometry to assess whole-animal metabolic rate; 3) collecting blood to assess plasma corticosterone as part of assessing stress; and 4) collecting blood from mice to assess two aspects of innate immune function: antimicrobial properties of blood and total white blood cell count.