Unfixed VLPs were used for immunogold labeling to limit antibody reactivity to the cell surface proteins. The particles were adsorbed on formvar coated nickel grids, stained with NiV specific primary antibody (hyper immune mouse ascites fluid, HMAF, obtained from Dr. P. Rollin, CDC) diluted in buffer (1% BSA in 0.05 M tris buffer) rinsed in wash buffer (0.1% BSA in 0.05 M tris buffer), stained with colloidal gold labeled goat anti-mouse secondary antibody (Jackson ImmunoResearch Laboratories), washed, and then negatively stained with 2% uranyl acetate for viewing by EM.