Transforming growth factor-beta (TGF-beta) has been reported to be involved in the pathogenesis of cardiovascular proliferative diseases such as hypertensive vascular disease, atherosclerosis, and arterial restenosis after angioplasty. We designed a 38-base RNA-RNA chimeric hammerhead ribozyme to cleave human TGF-beta1 mRNA as a gene therapy for human arterial proliferative diseases. In the presence of MgCl2, synthetic ribozyme to human TGF-beta1 mRNA cleaved the synthetic target RNA into two RNA fragments of predicted size. A control mismatch ribozyme, with one different base in the catalytic loop region, was inactive. RNA-RNA chimeric ribozyme (0.01-1.0 muM) significantly inhibited angiotensin II (Ang II)-stimulated RNA synthesis in a dose-dependent manner in human vascular smooth muscle cells (VSMC). The mismatch ribozyme did not affect Ang II-stimulated RNA synthesis in the cells. RNA-RNA chimeric ribozyme (1.0 muM) inhibited the proliferation of human VSMC in the presence of Ang II. RNA-RNA chimeric ribozyme (1.0 muM) significantly inhibited Ang II-stimulated TGF-beta1 mRNA and protein expression in human VSMC. These results indicate that the designed RNA-RNA chimeric hammerhead ribozyme targeted to human TGF-beta1 mRNA can effectively and potentially inhibit growth of human VSMC by cleaving the TGF-beta1 mRNA. This finding suggests that this ribozyme will be useful in the gene therapy of arterial proliferative diseases.