Arterial matrix proteoglycans (PG) are necessary for the maintenance of viscoelastic properties of the vessel wall, but excess levels, particularly of versican and biglycan in primary and restenotic intimal thickenings, are correlated with increased tissue volume and with atherogenicity. There is good evidence that the primary stimulus to increased PG synthesis, including versican and biglycan, is transforming growth factor-β<sub>1</sub> (TGF-β<sub>1</sub>). The aim of this study was to determine the effects of reducing endogenous TGF-β<sub>1</sub> on rates and patterns of PG synthesis and on versican, biglycan and decorin accumulation in vivo. Rabbit common carotid arteries subjected to balloon catheter injury were treated with a TGF-β<sub>1</sub> antisense phosphorothioate oligonucleotide applied in a pluronic gel to the adventitia. Control animals received a nonsense oligonucleotide or gel alone. TGF-β<sub>1</sub> antisense (1) significantly (p < 0.005) inhibited, at day 2, the balloon catheter-induced increase in TGF-β<sub>1</sub> mRNA relative to β-actin mRNA; (2) inhibited intimal thickening at 23 days by ∼40% (p < 0.05); (3) inhibited (p < 0.05) PG synthesis, measured by autoradiographic detection of [<sup>3</sup>H]glucosamine, in the media of day 2 ballooned carotids and in the subendothelial zone of day 23 neointima, and (4) decreased immunostaining intensity for versican (p < 0.03) and TGF-β<sub>1</sub> (p < 0.001) in the neointima. Biglycan was reduced to a lesser extent but not significantly and decorin was not affected. Proliferating cell nuclear antigen indices were variable and not significantly changed. These findings confirm a role for TGF-β<sub>1</sub> in developing neointima and demonstrate a specific effect on the synthesis, distribution, and accumulation of matrix PG, particularly versican.