The development of a Klebsiella serotyping method by counter-current immunoelectrophoresis (CIE) is described. Antisera were prepared against the capsular antigens of 72 type strains and tested for the specificity and strength of their precipitin reactions with antigens from homologous and heterologous serotypes. All antisera produced strong reactions with their homologous antigen: when diluted to titre 63 were highly specific, 3 cross-reacted strongly and 6 weakly with one other antigen. Pools of antisera for screening purposes were constructed on the basis of common crossreactions: component serotypes of each pool could be detected strongly and specifically. The technique is simple to perform, fairly rapid, and economical in the use of antisera. Results can be read easily and quickly and the intensity of cross-reactions compared directly. The technique appears to be more specific and is less time consuming than the Quellung method, but further assessment of its efficacy in typing routine clinical cultures is necessary.