The effect of human placenta hydrolysate (Laennec) on residual liver regeneration after about 70% partial hepatectomy (PH) in normal and CCl4-induced cirrhosis rats was examined. Both intravenous or subcutaneous injections of Laennec increased the regeneration rate of the residual liver after PH in normal rats. Intravenous injection of Laennec inhibited the decrease of liver total protein, and it decreased the level of serum transaminase (GOT, GPT). The regeneration rate of the residual liver after PH in CCl4-induced cirrhosis (CCl4-PH) rats increased by intravenous or subcutaneous injection of Laennec. Laennec also inhibited the increase of serum GOT caused by CCl4-PH. In the pathological examination of the regenerating liver, intravenous injection of Laennec minimized the pathological changes caused by PH or CCl4-PH such as vacuolation and necrosis in the hepatocytes. The enhancement of cytoplasma regeneration in hepatocytes was noticed by intravenous injection of Laennec, but that by subcutaneous Laennec was slight. Intravenous injection of Laennec also minimized the lipid deposition in liver caused by CCl4-PH. Laennec had no effect on the pseudolobule formation caused by CCl4. Thus, the effect of intravenous injection of Laennec on the liver regeneration in PH rats was much more potent than that by the subcutaneous injection.