The changing distribution of a nuclear envelope antigen recognized by a monoclonal antibody raised against human fibroblast vimentin during the syncytial mitoses of the Drosophila embryo has been studied with a confocal laser scanning microscope. The antigen appears very early as irregular aggregates in the peripheral cytoplasm of the preblastoderm embryo. As the first nuclei reach the periplasm the antigen is localized on the nuclear envelope and the cytoplasmic staining decreases. In addition to the perinuclear labeling we observed intense midzone and polar staining during the mitotic cycle. A possible relationship between polar localization of the antigen and centrosome position is discussed.