The pharmacologically active components of the plant Silybum marianum are the flavonolignans, silibinin and silichristin. It has been shown that these compounds can be used successfully in therapy to promote faster regeneration of diseased liver. The biochemical mechanism for this cell-regenerating power has been elucidated. It has been demonstrated that silibinin stimulates the activity of the DNA-dependent RNA-polymerase I, thus causing an increase in rRNA synthesis and an accelerated formation of intact ribosomes. The consequence of this stimulation is a general increase in the rate of synthesis of all cellular proteins. Molecular modelling revealed that silibinin may imitate a steroid hormone by binding specifically to polymerase I, thus stimulating the enzyme activity. The molecular mechanism described has been demonstrated in experiments with rat and mice liver in vivo, with hepatocyte cultures, isolated liver nuclei, and purified enzyme and receptor proteins in vitro. The increase in protein synthesis offers a good explanation for the liver-regenerating power of the plant extract. Similar results have been recently found with human and monkey kidney cells.