Plasma and pituitary extracts from hepatectomized mice as well as pure growth hormone, stimulate DNA synthesis in hepatocyte population of adult intact mouse liver. This effect is not observed with plasma and pituitary extracts from intact or sham operated mice. The corresponding effects on the litoral cell population of the liver follow the same pattern, but the results are not so clearcut as in the hepatocyte population. The possibility that growth hormone, released by STH cells of the pituitary, is one of the factors responsible for the stimulating effect of plasma during liver regeneration, is discussed on the basis of the present results and of those already reported in the literature.Facultad de Ciencias Médicas