Five healthy male adults were deprived of food for a short period (40 hr) and biochemical studies and urinalyses were done before and after fasting to determine the effects on liver and renal functions. Acceleration in lipid metabolism was seen with an increase of about 90% in NEFA and about 20% in TG. GOT, GPT and LDH showed elevations of about 40 to 100% indicating a slight effect of 40 hr fasting on liver functions. BUN, HDL-C and ALP showed increases of about 30% while, CPK and TC showed decreases of about 20%. In the other parameters changes of about 10% were seen. After a fasting with water intake of about 1,000 ml/day, a body weight loss of 1.2 kg was observed at 40 hr. During the short-term fasting (40 hr) as done in our study, changes were seen in glucose and lipid metabolism. However, since no abnormalities were seen in general biochemical parameters, we consider that a fasting of this duration is valuable for use as one of the fastings.