A comparative study was performed of dense 5 hour cultures of rat hepatocytes and equal density cultures of mesenchymal stromal cells (MSC) isolated from human adipose tissue of rat bone marrow. The cells were grown on collagen coated class slides in serum free medium. Unlike in hepatocytes, no rhythm of protein synthesis was initially revealed in MSC, but such a rhythm manifested itself when the culture medium was supplemented with melatonin (2 nM, 5 min). The results of experiments with cytoplasmic calcium che lator BAPTA AM and protein kinase inhibitor H7 indicate that the mechanism of protein synthesis synchro nization in MSC consists in calcium dependent phosphorylation of cell proteins.