The potential of immunogold-silver staining has been evaluated in immunoelectron microscopic studies of human normal peripheral blood lymphocyte subpopulations. The cells were labeled, before being embedded in resin, using 5 nm colloidal gold particles and this was followed by silver enhancement. The use of colloidal gold particles permits detection of small amounts of antigen; the silver intensification forms a sphere of heavy metal around the gold granule giving rise to an ultrastructural marker which can be easily seen even at low magnification. The ultrastructural details of the cells were well preserved and there was no significant background staining. The major advantage of the present IGS technique is that it permits a rapid and simultaneous evaluation of both the immunophenotype and the ultrastructural characteristics of cells.