Highly reproducible samples of T. spiralis larvae were obtained and maintained in vitro for 48 hr without loss of infectivity. Initial values for carbohydrates, as % dry weight, were: Total carbohydrate, 21.1; alkali-stable carbohydrate, 20.6; glycogen, 15.9; trehalose, 4.8; glucose, trace. Initial values for lipids were: Total lipids, 9.1%; phospholipids, 6.6; glycolipids, 0.8; neutral lipids, 1.7. Phospholipid fractions obtained by thin layer chromatography consisted of phosphatidylcholine, 52%; phosphatidylethanolamine, 20%; lysophosphatidylethanolamine, 12%; phosphatidylserine, 10%; and sphingomyelin, 6%. A glycolipid fraction obtained by column chromatography did not contain C,a or hydroxyacids. Neutral lipids included cholesterol, 48%; cholesterol esters, 9%; triglycerides, 20%; diglycerides, 7%; free fatty acids, 8%. Approximately one-half of the total lipid fatty acids were saturated. Unsaturated acids contained large amounts of C20:4 and C22:3 and were quantitatively dissimilar from mouse muscle acids. Thirty-seven acids containing from 10 to 22 carbons were identified by GLC and related methods. Glycogen and trehalose were rapidly utilized during aerobic and anaerobic in vitro incubation and formic, acetic, propionic, n-butyric, n-valeric, and n-caproic acids were excreted. Rates of utilization and excretion were unaffected by the presence of oxygen. The major volatile acid produced was n-valeric. Total lipids did not decrease during aerobic or anaerobic incubation, nor was there any change in their component fatty acids. Although the intermediary metabolism of Trichinella spiralis larvae has been the subject of a number of reports (see von Brand, 1966, for review), comparatively few details concerning their carbohydrates and lipids are known. The difference between glycogen content (12%; von Brand et al., 1952) and total carbohydrate (18.8%; Kurylo-Borowska and Kozar, 1960) may possibly be attributed to the presence of the alkali-stable disaccharide, trehalose, rather than to glucose or other reducing sugars (Fairbairn, 1958). von Brand and co-workers reported that glycogen stores were greatly depleted during a 40-hr survival period in vitro and that the rate was independent of the presence of oxygen. They also identified as fermentation products, by means of column chromatography, acetic, n-valeric and n-caproic acids, plus minor amounts of 2and 3-carbon acids. No analysis of trichinella lipids was undertaken in their investigation, other than to report that a substantial decrease in total lipids occurred under aerobic, but not under Received for publication 16 August 1968. * This work was supported by Grant No. AI-04953 and Training Grant No. 5 TOI AI-226, from the National Institute of Allergy and Infectious Dis-