The changes in the protein profile in cultured human myoblasts after induction of differentiation was studied by proteomic techniques (a combination of O'Farrell two-dimensional electrophoresis and subsequent protein identification by MALDI-TOF MS and MS/MS analyses). Forty-one proteins have been identified, 25 of which were present in both proliferating and differentiating myoblasts, which allows them to be considered as myoblast housekeeping proteins. The changes in the distribution of some isoforms of tropomyosins, S100 proteins, cofilin, etc. have been revealed. The possible role of these changes in the cell protein profile in the realization of the program of skeletal muscle cell differentiation is discussed.