Cross precipitin reactions of type sera of the Klebsiella group could take place with K and O Klebsiella antigens. The cross precipitin reaction due to O antigen could be eliminated by diluting type antigens, because of low antigen titers. When diluted type sera were used, many cross reactions due to O and K antigens were removed, although it was difficult to remove cross reactions from all type sera. However, all the type sera became type-specific by absorbing with cross-reacting K and O antigens, and could be used for the identification of Klebsiella types. Thus, type 12 antigen was found to consist of type 29 and 41 antigens, and was doubtful to be regarded as an independent type. Type 37 antigen was very similar to type 22 antigen.