Activins are dimeric growth factors composed of subunits, four of which have been isolated so far. While activin_A and_B are expressed in many tissues, the expression of activin_C and_E is confined to the liver. To date no biological role or activity has been assigned to activins formed from_C or_E subunits (activin C and E). Since activin A (_AA), among its various functions in other tissues, appears to be a negative regulator of liver growth, we hypothesized a similar role for activin C and E. Using a non-viral gene transfer system we specifically delivered genes encoding activin_C,_E, or_A to the mouse liver. mRNA analysis and reporter gene co-expression both indicated a reproducible temporal and spatial transgene expression pattern. The effects of activin overexpression were studied in the context of a regenerative proliferation of hepatic cells, a result of the tissue damage associated with the hydrodynamics based gene transfer procedure. Activin_C,_E, or_A expression, all temporarily inhibited regenerative DNA synthesis of hepatocytes and non-parenchymal cells, though to a varying degree. This first report of a biological activity of activin C and E supports an involvement in liver tissue homeostasis and further emphasizes the role of the growing activin family in liver physiology.