Surface immunoglobulin allotypes on rabbit peripheral blood lymphocytes (PBL) and spleen lymphocytes are detected by an immunoferritin labeling technique for electron microscopy. Human red blood cells, chemically coated with purified rabbit IgG of specific allotypes, served as test cells to assess the labeling specificity and efficiency. Immunoelectron microscopic labeling reveals that groups a, b, d and e allotypic specificities are readily detectable on passively coated test cells. However, only a and b group markers are detectable on lymphocytes. On rabbit PBL both a (VH of Fd region) and b (kappa chain constant region) group allotypes are detectable (73-78% and 68-77%, respectively); on spleen cells, 46% and 52-55% are positive for a and b locus allotypes, respectively. The d and e allotypes (i. e. gamma chain-specific) are undetectable on PBL or on spleen lymphocytes using this method. We conclude that the d and e group allotypes are either not present on the lymphocyte surface or are buried in the surface membrane and unacessible to the antisera used in this immunoferritin labeling technique.