Antibodies previously used for immunofluorescence localization of a myosin heavy chain-like polypeptide to the nuclear envelope in higher eukaryotic cells crossreact with both muscle and nonmuscle isoforms of Drosophila myosin heavy chain. Analyses of Drosophila tissue culture cells and premyogenic embryos suggest that it is the nonmuscle isoform that is associated with the nuclear envelope. Further immunofluorescence and immunoelectron microscopy indicate that this polypeptide is associated with nuclear pore complexes. These data support the hypothesis put forward previously that myosin or myosin-like molecules play a role in pore complex architecture.