482 Klebsiella pneumoniae and K. oxytoca strains isolated from different sources (human clinical material, feces of healthy subjects, sewage) were investigated for expression of MS-(mannose-sensitive) and MR/K-(mannose-resistant, Klebsiella-like) hemagglutinins. Regardless of the source of isolation, the majority of K. pneumoniae strains induced mannose-sensitive hemagglutination, but very few K. oxytoca isolates produced this type of hemagglutinin. In both species, most strains induced MR/K-hemagglutination. In general, environmental isolates showed a lesser incidence in production of each hemagglutinin and a higher percentage of non-hemagglutinating strains than fecal and clinical strains. These results suggest clinical isolates to be phenotypically more related to fecal than to environmental strains.