The ferritin-labelled antibody technique has been applied to the study of the distribution of the H-2 antigen. Using a specific antiserum for the isoantigens determined by the H-2dallele (H-2banti H-2d), the H-2 isoantigens were shown to be evenly distributed on the cell surface of lymphocytes, polymorphonuclear leukocytes, eosinophils, platelets, and erythrocytes. Lymphocytes were shown to possess the largest concentration of antigen at the cell surface. In preliminary experiments, nonspecific attachment of the ferritin-antibody marker to the intracellular components of dead or formalin-treated cells prevented the demonstration of an intracellular distribution of the H-2 antigen. The potential application of the ferritin-labelled antibody technique to the study of single H-2 isoantigenic specificities is discussed.