SummaryIt has been shown by others that partial hepatectomy in one partner of parabiotic rats induced mitoses in liver of the other, intact parabiont. We found previously that growth of transplanted tumors was enhanced by partial hepatectomy of the host. In this paper stimulation of non-malignant growth following partial hepatectomy in the rat is reported. Mitotic rate in cornea, and compensatory hypertrophy of kidney is increased. In hypophysectomized rats partial hepatectomy is followed by increased width of tibial epiphysis. These findings are discussed with regard to organ specificity and mechanisms of growth regulation.