The techniques of pre- and post-embedding immunocolloidal gold electron microscopy were tested for their usefulness for analyzing the morphogenesis of human immunodeficiency virus (HIV) strain LAV employing U-937 cells persistently infected with the virus (U-937/LAV). By both techniques the following results were obtained. (1) Budding process was restricted to a localized area at the membrane adjacent to the Golgi apparatus. (2) The distribution of viral envelope antigens was restricted to the electron-dense crescent structures on the cell surface. (3) Virions released from the cells could be classified mainly into 2 categories: virions with doughnut-shaped cores or with conical cores at the center of the particles. And p24 proteins localized on the thick electron-dense cores of both types. These findings support the idea that pre- and post-embedding immunogold electron microscopy is very useful for studying the morphogenesis of viruses.