Inducing pulmonary edema in rat, air bubbles the diameter of which was about 0.3 mm were continuously infused into the right atrium through a catheter at the rate of 2.8 ml/kg/hr during 0.5, 1 and 2 hours, under controlled ventilation (tidal volume of 9 ml/kg and respiratory rate of 80/min) with 1% halothane in room air. Saline or Dilazep hydrochloride solution was simultaneously infused into the right atrium via another catheter. Pulmonary edema was evaluated by the measurement of the ratio of extravascular water weight of lung (g) to blood-free dry lung weight (g) (EVWW) using the gravimetric method and with histologic studies using the rapid freezing method. In control rats, which were sacrificed immediately after induction of anesthesia, the EVWW was 3.114 +/- 0.121 g/g blood-free dry lung (mean +/- 1 S.D. n = 8). In baseline experiments (2 hours ventilation and saline infusion without air embolization), the EVWW was 3.291 +/- 0.081 (n = 4). In air embolization groups with 2 hours saline infusion, EVWW were 3.756 +/- 0.170 (n = 4), 3.722 +/- 0.170 (n = 4) and 3.731 +/- 0.245 (n = 5) in 0.5, 1 and 2 hours infusion groups, respectively. Regardless of emboli infusion time perivascular cuffs and peribronchial cuffs were revealed in the 2 hour saline infusion groups. In the experiment in which the animals were sacrificed immediately after one hour infusion of air bubbles, there was no evidence of pulmonary edema and the EVWW of 3.060 +/- 0.092 (n = 4) in this group control and baseline were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)