1. Serotonin (5-HT), as a type of mitogen for smooth muscle cells, plays an important role in the development of pulmonary hypertension. It is known that selective serotonin re-uptake inhibitors (SSRI) inhibit 5-HT internalization. Therefore, the aim of the present study was to investigate the protective effect and mechanism of the SSRI sertraline against pulmonary hypertension. 2. Monocrotaline (MCT)-induced chronic 'inflammatory' pulmonary hypertension in Wistar rats was established. Pulmonary haemodynamic measurement and lung tissue morphological investigations were undertaken. Serotonin transporter (SERT) mRNA was assayed by reverse transcription-polymerase chain reaction (RT-PCR). 3. The results showed that pulmonary artery pressure (PAP) was significantly increased by MCT treatment from 12.6 +/- 2.1 to 20.1 +/- 3.4 mmHg (P < 0.01 vs control) and sertraline attenuated the MCT-induced increase in PAP from 20.1 +/- 3.4 to 16.4 +/- 1.8 mmHg (P < 0.05 vs MCT). The right ventricular index was increased in the MCT-treated group from 0.32 +/- 0.04 to 0.51 +/- 0.09 (P < 0.01 vs control) and was reduced to 0.42 +/- 0.04 by sertraline (P < 0.05 vs MCT). The degree of muscularization of the pulmonary artery in the MCT-treated group was significantly higher than control (P < 0.01) and was decreased by sertraline (P < 0.01 vs MCT). The RT-PCR assay showed that MCT increased SERT mRNA expression from 0.86 +/- 0.08 to 0.99 +/- 0.06 (P < 0.05 vs control), which was attenuated by sertraline (0.82 +/- 0.09; P < 0.05 vs MCT). 4. In conclusion, the SSRI sertraline protects against MCT-induced pulmonary hypertension by decreasing PAP, right ventricular index and pulmonary artery remodelling, which may be related to a reduction in SERT mRNA.