Genes I3 and A2 of the vaccinia virus strain L-IVP DNA were cloned into bacterial expressing vectors. The monospecific antisera to the expression products of these genes in E. coli were obtained. By means of immunochemical cross-analysis two polypeptides of equal electrophoretic mobility were found in the virion preparations in the band of the major envelope protein p35. The major of them is the product of gene I3, and the minor is encoded by gene A2.