The in vivo effect of transforming growth factor-beta 1 (TGF-beta 1) was studied in a model system in which arterial intimal thickening was induced by injury of rabbit arteries with a balloon catheter (BCI). Intimal area and its ratio to medial area in carotid arteries after BCI were significantly higher in rabbits treated with 10 micrograms/kg TGF-beta 1 and 10 mg/kg aspirin i.v. QD (TGF-beta 1 group) than in those treated with 10 mg/kg aspirin i.v. QD only (control group). Intimal cell numbers in the TGF-beta 1 and control groups were not significantly different from each other, but matrix volume in the intimal layer was significantly higher in the TGF-beta 1 group. By immunohistochemical and Northern blot analyses, the fibronectin content in carotid intimal and medial layers was greater in the TGF-beta 1 group compared with that in the control group. Thus, in intimal thickenings induced by BCI. TGF-beta 1 mainly enhanced the formation of matrix containing fibronectin. Moreover, the mRNAs of TGF-beta 1 and type II receptors were detected in carotid arteries 7 and 14 days after, but not before, BCI. Thus, TGF-beta 1 influences the process of intimal thickening induced by BCI through a receptor-mediated mechanism in vivo. The significance of this fact is discussed in relation to the development of atherosclerosis.