Amino acid, carbohydrate, and lipid components of cell walls of Brucella abortus strain 19A (low virulence) and strain 2308 (high virulence) were compared by thin layer chromatography (TLC) and by use of an amino acid analyzer. A total of 15 amino acids were detected by both chromatographic methods. Each amino acid was present in greater amounts in strain 2308 than in strain 19A when equal amounts of hydrolysates of cell wall and endotoxin-containing preparations were analyzed. A component with the same R, value as ethanolamine was present in strain 2308 cell wall hydrolysates but was not revealed by TLC of strain 19A cell wall hydrolysates. This component was not detected with the amino acid analyzer. TLC of cell walls tagged with 2 ,4-dinitrofluorobenzene prior to hydrolysis showed that phenylalanine was a terminal amino acid in cell walls of B. abortus strains 19A and 2308, B. suis strain 1776, and B. melitensis strain 2500. Carbohydrates detected in cell walls of strains 19A and 2308 by TLC were tentatively identified as glucose, mannose, rhamnose, and galactose. Colorimetric tests were also positive for 2-keto-3-deoxyoctulosonic acid, heptose, and dideoxyhexose. At least seven lipid components were detected by TLC of ether extracts of cell walls of strains 19A and 2308. It is suggested that one or more lipids is important in maintaining cell wall structure, because isolated cell walls rapidly became fragmented after exposure to ether.