Evidence is presented that virion-derived antigens as well as viral antigens expressed on cell surfaces after infection, may participate in the formation of "target-antigen complexes" (TACs) which render vaccinia virus-infected cells susceptible to recognition and killing by syngeneic, vaccinia virus-specific cytotoxic T cells (VV-CTLs). By employing L cells infected with trypsin-treated and untreated virions, evidence was obtained that proteins with molecular weights of 32K and 37K may be among the virion-derived antigens which participate in TAC formation. Following virus infection, a sequential expression of virus-specified antigens on the plasma membrane of infected cells could be detected. At 1 hr p.i., polypeptides with molecular weights of 48K-50K and 36K-37K were present on infected cell surfaces; by 2 hr p.i., polypeptides with molecular weights of 48K-50K, 42K-44K, 36K-37K, 29K-30K, and 16K-17K were detected on plasma membranes. As measured by in vitro, 51Cr-release assays, vaccinia virus-infected L cells were completely susceptible to lysis by VV-CTLs (greater than or equal to 50% measured specific lysis) when (a) "early" but not late viral functions were expressed as measured with virus-infected cells which had been treated with hydroxyurea (5 X 10(-3) M) to block DNA replication or (b) when active protein synthesis was allowed to proceed for 90 min postadsorption and the infected cells were then treated with cycloheximide (100 micrograms/ml) to block further protein synthesis. Under these experimental conditions, polypeptides with molecular weights of 58K, 48K-50K, 42K, 36K-37K, 34K, 32K-33K, 27K-29K, and 16K-17K were expressed on the plasma membranes of vaccinia virus-infected cells but not uninfected cells. Whether each of the virion-derived and (or) virus-encoded polypeptides can associate with Class I, major histocompatibility antigens on the surfaces of virus-infected cells to form a primary or cross-reacting TAC recognized by VV-CTLs remains to be investigated.