The major hepatic reaction which occurs in response to degeneration or partial loss of the liver is compensatory hyperplasia. After finding out that hemodynamic factors have no influence in hepatic regeneration, the investigations have been focused on some trophic factors which have been found in the blood and which have been believed to provide the basic control of regeneration. In our controlled experimental study we have tried to evaluate the effects on hepatic regeneration of cyclosporin and somatostatin which are known to act on the hepatic regeneration ability or which are thought to have effects on regeneration because of their mechanism of action. For the purpose of evaluating the regenerative response findings like the weight of the regenerated liver, mean Ag nuclear organizer region (AgNOR) number, the mitosis index, cells with double nuclei and hyperchromatic nucleus were taken into consideration. The results of the cyclosporin group were higher than of the controls, but there was no statistically significant difference between them. In the somatostatin group, an inhibition of regeneration related to the dose and to the duration at the beginning and a delayed augmentation of the regeneration rate due to the withdrawal of the drug were observed. Values of AgNOR were significantly higher compared to the control group on the 5th day postoperatively, while the liver weight was lower on the 1st day (p < or = 0.05).