Interaction between human leukemia cell and Ureaplasma urealyticum was investigated light and electron microscopically. The cells adhered with their pseudophodia to the surface of colonies of Ureaplasma urealyticum. A large number of pleomorphic Ureaplasma urealyticum adhered to the cell surface and were seen in the intracellular vacuoles. Ureaplasma urealyticum was captured by the villus-like structure of the cells and actively phagocytized.