We previously reported that mean pulmonary arterial pressure (Ppa) during pulsatile flow exceeded that for steady flow when flow was greater than the normal resting value and speculated that this was due to irregularities of the flow profiles in precapillary vessels, mainly the larger arteries. From this we hypothesized that neither mean microvascular pressure nor the rate of fluid filtration would be affected by flow pulsatility. We therefore compared the effects of steady vs. pulsatile flow on the double-occlusion pressure (Pdo) and on edema formation (rate of weight gain) in zone 3 rabbit lungs. Excised left lungs (n = 19) were perfused with Tyrode solution and ventilated with an end-expiratory pressure of 2.5 cmH2O. A diaphragm pump generated pulsatile flow with a stroke volume of 1.0 ml (approximately 0.8 the normal resting value for rabbit left lung). Nonpulsatile flow was generated by raising an arterial reservoir. Flow rate was set at 100 or 400 ml/min (approximately 0.4 or 1.6 x the normal resting cardiac output, respectively). Vascular pressures (referenced to the bottom of the lung) were measured after ventilation, at end expiration, was interrupted. Pdo values were obtained in random order at 15 time points that were evenly distributed within the pulse cycle, averaged across pulses to obtain the mean capillary pressure profile, and then averaged over time. At the lower flow of 100 ml/min, mean Ppa and Pdo were slightly lower (3-4%) during pulsatile compared with nonpulsatile conditions. At the higher flow of 400 ml/min, mean Ppa was higher under pulsatile conditions (13%), whereas downstream the mean Pdo values were equal.(ABSTRACT TRUNCATED AT 250 WORDS)