We describe a technique for the estimation of pulmonary capillary pressure from arterial pressure profiles recorded during occlusion of blood flow in a quasi-intact dog lung preparation. In this preparation, the lower lobe of the left lung was perfused directly by the right ventricle while its venous outflow was collected in a reservoir before being recirculated into the animal. Arterial occlusion maneuvers were accomplished by inflating the balloon of a Swan-Ganz catheter positioned in the left lower lobe artery. The instant of occlusion was precisely determined as the time during the balloon inflation when the pressure inside the balloon reached a maximal value. The arterial pressure profile recorded after inflation of the Swan-Ganz balloon was analyzed in the following manner to estimate the capillary pressure: first, a single exponential approximation of the pressure decay was computed over a short segment of the postocclusion pressure data. The extrapolation of the exponential fit toward the instant of occlusion (Pa0) yielded a first estimate of the capillary pressure. A second estimate was selected as point at which the pressure tracing merged with the exponential fit (Pa0+). These estimates were compared to the double occlusion pressure, which was used as a reference value of the capillary pressure (Pcap). Our results show that the extrapolation of the exponential fit toward the instant of occlusion gave an accurate estimation of the pulmonary capillary pressure over a wide range of pressures: Pa0 = 0.95 (+/- 0.04).Pcap, and the slope of this relationship was not statistically different from 1.(ABSTRACT TRUNCATED AT 250 WORDS)