Proteins of wild-type phate T4 and its mutants in genes rII, su(30), stII, stIII, rVI-39 and 60 are studied by means of polyacrylamide gel electrophoresis in the presence of sodium dodecylsulphate of membrane fractions and lysates of infected bacteria. Physiological studies of mutants in these genes carried out by the authors and other investigators allow to suggest that when functions are realized, the products of these genes interact with the plasmatic membrane of the infected bacteria. The product of rIIB cystrone has been indentified as the protein of the membrane of an infected bacterium, its molecular weight being about 30 000. The products of genes su(30), stII, stIII and rVI could not be identified either in lysate or in membrane fraction. The function of gene stII is "superstoichiometric", which may be due to the involvement of a very small product amount when the function of gene stII is realized. Mutants in genes 39 and 60 lack one and the same protein with molecular weight of about 40 000 which is a protein of the membrane of an infected bacterium. This protein may be a product of gene 39, and the functional product of gene 60 is necessary to synthesize it.