We recently reported (Pereira et al., Proc. Natl. Acad. Sci. U.S.A. 78:5202-5206, 1981) that herpes simplex virus 1 and 2 glycoproteins, previously designated gA and gB, could not be differentiated by a bank of independently derived type-specific and type-common monoclonal antibodies. We also reported that from lysates of infected Vero cells, all but one monoclonal antibody precipitated gA/B glycoproteins which had faster electrophoretic mobility than the corresponding infected HEp-2 cell glycoproteins and a set of three small polypeptides which we designated g(A + B) reactive polypeptides 1, 2, and 3. Antibody H368, the single exception, failed to react with the gA/B glycoproteins or related antigens accumulating in infected Vero cells. In this paper, we report the following results. (i) The high-apparent-molecular-weight gA/B glycoproteins accumulating in infected HEp-2 cells were cleaved by a proteolytic enzyme contained in Vero cell lysates to yield more rapidly migrating proteins that were indistinguishable from authentic Vero cell gA/B glycoproteins. Like its authentic counterpart, the cleaved gA/B glycoproteins failed to react with H368 monocolonal antibody. In addition, the lysate cleaved HEp-2 cell gA/B glycoproteins into g(A + B) reactive polypeptides 2 and 3. (ii) The proteolytic activity contained in the uninfected cell lysates was inhibited by N-alpha-p-tosyl-l-lysine chloromethyl ketone and is therefore trypsin-like. (iii) Pulse-chase experiments indicated that the cleavage of gA/B glycoproteins occurred during or soon after translation but that the accumulation of g(A + B) reactive polypeptide 1 was a consequence of a delayed processing event. (iv) Analysis of herpes simplex virus 1 x herpes simplex virus 2 recombinants indicated that the determinants of type-specific immune reactivity and electrophoretic mobility of gA/B glycoproteins and g(A + B) polypeptides map near the right terminus of herpes simplex virus 1 BamHI-G.