Several rat models of pulmonary hypertension have been developed. However, up until now it has been difficult to monitor pulmonary arterial pressure for long periods of time. The goal of the present study was to develop a telemetry system allowing chronic monitoring of pulmonary arterial pressure in freely moving rats. For this purpose, while animals were under anesthesia, a sensing catheter was implanted into the pulmonary arterial trunk through the right ventricle. This catheter was connected to an emitter implanted in the abdomen. Validation of the system was performed in three steps. First, acutely, we controlled that the pressure signal transmitted by the telemetry system was accurate and corresponded to a signal obtained with a high-fidelity Millar catheter. Second, we evaluated the chronic consequences of implantation of the system. Third, we used the system to monitor pulmonary arterial pressure in a model of monocrotaline-induced hypertension in which the effects of bosentan, an endothelin-receptor antagonist, were evaluated. The telemetry system was reliable and did not lead to damage of the right ventricle and/or to chronic pulmonary embolism. After a recovery period of 8-10 days, mean pulmonary arterial pressure was stable. With the use of this telemetry system, it was possible to follow the increase of pulmonary arterial pressure induced by monocrotaline. In this model, bosentan decreased mean pulmonary arterial pressure by 13% (P = 0.07), suggesting a role of endothelin in this model of pulmonary hypertension. We conclude that it is possible to use this telemetry system to monitor pulmonary arterial pressure in freely moving conscious rats.