Despite great advances in analysing hemodynamic, morphological and biochemical changes during the process of liver regeneration, the exact (patho)physiological mechanism is still unknown. A short survey of literature is given of the kinetics of liver regeneration and the significance of different hepatotrophic factors. A distinction is made between factors promoting cell hypertrophy and factors stimulating hyperplasia. Loss of cell-cell contact inhibition, metabolic overload or elimination of inhibitory substance are discussed as trigger mechanisms for cell proliferation after partial hepatectomy (PH). Trophic factors like insulin may create optimal conditions for cell growth. The Hepatic Stimulatory Substance (HSS) of LaBrecque is probably the most purified proliferation factor at present, but there are several claims for other hepatotrophic factors too.