The ultrastructure of flagella of enteropathogenic E. coli was analysed by electron microscopy. The flagella of E. coli 0126, 026, 0114 and 0128, each of which have different H antigen types, were tentatively classified into four types according to their ultrastructural similarity. The appearence of most flagella structures were homologous in each H type and identical with a previous report (Lawn, AM, 1977). However, the structure of H31, H25 and H48 were different from the previous ones and H11 (026K60) and H25 (026K60) showed two different types of flagella structure in a single H type. Immuno-electron microscopy using gold-labeled anti-rabbit IgG goat antibody disclosed that there were anti H type sera reactive flagella and non reactive flagella in both Hll and H25, although the molecular weight of each flagellin showed one homologous band by SDS-PAGE. The result suggests that there is a certain diversity in the manner of self assembly of flagellin to form flagella structures.