Lactoperoxidase-catalyzed radioiodination was used to study reactions between surface antigens and antibodies on BHK-21 cells infected with HSV-1 and HSV-2. Isolation of iodinated surface antigens was achieved by indirect immune precipitation of Triton X-100 disrupted cells with antisera to HSV and IgG. Analysis of immune precipitates by polyacrylamide gel electrophoresis (PAGE) revealed at least 10 antigens, ranging in m.w. from 35 x 103 to 160 x 103 daltons. Antigens were detectable on cell surfaces as early as 2 hr post-infection. Electrophoretic patterns of surface antigens induced by HSV-1 were similar to those induced by HSV-2. In both cases the major portion of activity was associated with glycoprotein(s) in the range of 115 x 103 to 130 x 103 daltons. A reduced amount of radioactivity was obtained if cells were reacted with anti-HSV sera before disruption with Triton X-100, suggesting that less surface antigen was accessible to HSV antibody applied directly to intact cells.