Naturally occurring lysophosphatidylcholine (LPC) has effect on many different cell proesses, such as monocyte chemotaxis, smooth muscle cell contraction, platelet activation and the secretion of growth factors from endothelial cells. In this study, examination was made of the effects of exogenous LPC on DNA synthesis in human dermal fibroblasts, NB1RGB. DNA synthesis was accelerated by C_{12 : 0}-, C_{14 : 1}- and C_{16 : 1}-LPC, all of which were previously shown to enhance the synthesis of glycosaminoglycan (GAG, mainly hyaluronic acid). C_{18 : 3}-L, PC possessing activity for GAG synthesis greatly repressed that of DNA. DNA synthesis enhanced by C_{12 : 0}-LPC failed to occur due to the presence together of staruosporine, genistein, islet-activating protein (IAP) and propranolol. Neither was there any GAG synthesis which had been enhanced by C_{12 : 0}-LPC and C_{18 : 3}-LPC, due to these inhibitors except for propranolol. Phosphatidylethanol had no effect either on DNA or GAG synthesis. Depressed DNA synthesis by C_{18 : 3}-LPC was not restored by IAP. The activation of adenylyl cyclase would thus appear unrelated to the depression of DNA synthesis.