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It is frequently necessary to postpone chemical analyses of biological materials for long periods of time. Many such materials contain a large amount of water and dehydration is desirable from the point of space economy, especially when large amounts of the materials are to be stored. Often, biological materials are more conveniently handled and accurately sampled in the dry state, since they can be pulverized and thoroughly mixed. I n our laboratory, we were concerned with determining the nitrogen, fat, calories, and amino acid content of certain foods and of human feces. It was not desirable to add acid to homogenates of this material because caloric and tryptophan values were among the analyses t o be done.The present study was undertaken t o show ( a ) whether or riot there is an appreciable loss of nitrogen aiid volatile fatty acids as ii. result of drying at the natural p H of biological materials, and (b) to compare cominon methods of drying for differences in the effect of desiccation on nitrogen and fat contents of such materials. Three foods were selected for carrying out these experiments-ground beef , hoinogenized cow's milk, aiid whole eggs. Each of these foods was dried in four ways-air oven, vacuum oven, infrared lamps, and lyophilizer. EXPERIMENTAL Preparation of samples for drying. Twenty-four whole eggs were put i n a Waring Blendor and homogenized; eighteen approximately 35-g. samples were put in 6-inch uncovered Petri dishes that had been weighed previously. Eighteen 45-g., replicate samples of homogenized milk and eighteen 70-g. samples of ground beef wcrc put in dishes for drying. Samples of similar corresponding sizes were put into weighed flasks to be lyophilized. The weight of food plus container was determined in each case.Drying procedures. Six samples of each kind of food were put in the air oven a t a temperature of 80" C., in the vacuum oven at 61" C., and in the path of infrared rays at an average temperature of 51" C. Three samples of each kind of food were lyophilized at -75" C. and 150 microns pressure. All samples were dried until two successive weighings agreed within 2 mg. The dried samples were ground, transferred to bottles, and stored a t -29" C. until analyzed. All analyses were eonipletetl within 3 months after drying. Chemical analyses. Total nitrogen was determined by the Kjeldahl methotl (1). Packets of Kel-Pak Powder No. 1, consisting of K~SOG CuSO1, and HgO, were used a This investigation was supported in part by funds received from the R. I,. Smith Foundation.Present address: General Electric Co.,