Primary cultures of rat hepatocytes were studied in serum-free medium. Ultradian protein synthesis rhythm was used as a marker of overall cell synchronization and cooperation amongst the population. The level of synchronization was determined by amplitudes of the rhythm. Low synchronization of old rat hepatocytes can be enhanced by addition of either gangliosides or phenylephrine to the medium. Incubation of cultures with gangliosides lasted for 2.5 h, while action of phenylephrine was only for 2 min. The amplitude of protein synthesis rhythm was increased 1.5–2 times. In cultures transferred to a fresh normal medium, this increased amplitude was observed for at least 2–3 days. Thus, both gangliosides and phenyleprine are triggers, which, as shown earlier, initiated calcium-dependent processes in the cytoplasm. The results are discussed in the light of concept of the cell self-organization by a direct cell—cell communication.