We have developed a micropuncture technique for the measurement of microvascular pressure in the intact lung of rabbit. We anesthetized 16 rabbits (halothane, 0.8%) and mechanically ventilated them through a tracheotomy. Then, we exposed the right lung by rib resection over the right anterior chest. We measured pulmonary artery, left a trial, and systemic pressures by direct catheterization and cardiac output by the thermodilution technique. For micropuncture, we stabilized the lung on a shelf and stopped ventilation for 3-4 minutes at an airway pressure of 7 cm H2O. We injected pancuronium intravenously to paralyze the diaphragm and intercostal muscles. Of the total pulmonary vascular pressure drop, 52% occurred in the microvascular segment between arterioles and venules of 20 μm diameter, 28% occurred in the arterial segment, and 20% occurred in the venous segment. We conclude that in the intact lung of rabbit, the major pressure drop occurs in the microvascular segment.