Two strains of Ixodes spirochetes, one isolated in the United States (B31) and the other in Sweden (G25), were examined by electron microscopy. Cells of strain G25 were 11-25 micron long with a wavelength of 2.1-2.4 micron and an amplitude of 0.4 micron. Eleven flagella were inserted subterminally at each end of the cell. Cells of strain B31 were similar but had eleven or seven flagella. Cytoplasmic tubules were not seen in cells of either strain. Although not identical, both strains showed ultrastructural details characteristic of the genus Borrelia.