The capsular polysaccharide of Klebsiella serotype K74 belongs to a chemogroup consisting of seven strains, of which four contain 1-carboxyethylidene groups (pyruvic acid acetals). The polysaccharide from K74 is demonstrated to be of the "3 + 2" type, and to be based on the repeating unit shown (Formula, see text). The capsular polysaccharide from Klebsiella K74 is composed of D-glucuronic acid, D-galactose, and D-mannose, and this chemotype includes a total of seven strains, of which four have 1-carboxyethylidene groups (pyruvic acid acetals). In this chemogroup, the structures of the capsular polysaccharides of the serotypes K20 (ref. 3) and K21 (ref. 4) have been published.