Sedimentational fractionation of asynchronic Ehrlich ascitic cells po¬pulation was carried out according to cell cycle phases. Separation of tumor cells suspension was carried out under 1 g in 0–0,3 M sucrose concentration gradient. Cells, pituated in S phase, were selected to 3 fractions in early, midle and late S phase respectively. It was studied temporal order replications of synchronized Ehrlich ascitic cells. It was shown that the replication of oncogene c-myc beginning in early S phase.