OBJECTIVE: To study the levels of Tenascin (TN) mRNA in pulmonary vascular remodeling associated with pulmonary hypertension(PH) induced by monocrataline (MCT). METHODS: SD rats were randomly assigned into the control (CON) group and MCT group. The model of PH was created by injecting hypodermatic MCT. Rapid competitive RT PCR was used to examine the levels of TN mRNA in central pulmonary arteries (PAs) and lungs at different times after MCT or NS injections. RESULTS: Increased expression of TN mRNA was detected 7 days after the injection of MCT. The expression of TN mRNA in lungs of the MCT group (0.56±0.08) was higher than that of the CON group (0.29±0.04)，P<0.01. TN mRNA in PAs of the MCT group (0.57±0.05) was higher than that of the CON group (0.30±0.04)，P<0.05. The increase of the level of TN mRNA preceded the elevation of pulmonary pressure (14 days) and continued to increase with the rising of pulmonary pressure. CONCLUSIONS: TN might be involved in the pathogenesis of pulmonary vascular remodeling with PH.