Here we produced a monoclonal antibody (termed as mH2) which specifically recognized an 86-kD subunit of Human DNA helicase II (p86) in HeLa cells. Immunohistochemical analysis of p86 throughout the cell cycle showed that its localization was changed from the nuclei to the cytoplasm, when the cells entered into prophase, and p86 localized diffusely in the cytoplasm during mitosis. Double staining of interphase HeLa cells with mH2 and an antibody, which recognized a component of nuclear pore complex, showed that p86 did not localize at the nuclear envelop in interphase cells.