In this study we investigated the applicability of the (silver-enhanced) immunogold labeling method for atomic force microscopy. Human lymphocytes were labeled with anti-CD3 conjugated to fluorescein isothiocyanate and a secondary antibody (goat anti-mouse) linked with 1- or 30-nm colloidal gold particles. Silver enhancement was applied on these labeled cells to increase the size of the labels. In a setup combining an inverted optical microscope and a stand-alone atomic force microscope, a direct correlation was made between the force and the fluorescent images. Additionally, we performed how cytometric analysis. From the results we conclude that immunogold labeling using small labels (1 nm) in combination with silver enhancement (30 min) proves to be a reliable method for high-resolution cell surface antigen detection in atomic force microscopy. (C) 1994 Academic Press, Inc.