The arginine and its metabolites were used to investigate the effect on organotypic tissue culture of explants from the spleen, liver, brain cortex and heart of young (3-month old) and aged (18-month old) rats. The arginine effective concentration was 0.5 ng/ml, showed proliferative effect in spleen, liver tissue cultures as compared to the control explants in both groups of rats. No effect of arginine was observed in nervous tissue culture in both groups of rats. The arginine and its metabolites--citrulline, ornitine, urea--stimulate the cell proliferation in miocardium explants in young rats, but not in old. The nitric oxid inhibits the heart explants in young rats.