OBJECTIVE: To explore the etiology of pulmonary hypertension with relation to the pulmonary expression of matrix metalloprotease1 (MMP 1). METHODS: The pulmonary hypertension animal models were induced by monocrotaline (MCT), the pulmonary arterial pressure was measured by cathetrization, and the pulmonary MMP 1 mRNA expression was studied by RT PCR. RESULTS: The pulmonary arterial pressure increased significantly in the 3rd week after the induction of MCT and reached the peak in the 4th weak; the pulmonary MMP 1 mRNA expression increased significantly in the 2nd week and then decreased greatly in the 3rd week, and still it was higher than that in the 1st weak. CONCLUSIONS: Changed MMP 1 expression might play a part in the development of pulmonary hypertension. MMP 1 overexpression might play the role of target during the earlier stage of pulmonary arterial remodeling.