We evaluated the density distribution (anterior-posterior) of the right lung in 19 acutely anesthetized supine dogs using computed transmission tomography (CTT). Eleven dogs served as controls, and eight received 0.12 cc/kg of intravenously administered oleic acid. The latter were sequentially imaged over 1 hour. Nine of these dogs (three control and six oleic acid dogs) had wet weight/dry weight ratios of the corresponding anterior and posterior lung sections evaluated immediately upon completion of the scans. In the control animals, the posterior (dependent) lung was 25 +/- 8% (+/- S.D.) denser than the anterior lung, and did not differ if a second section of the lung was evaluated (1 cm cranial or caudal), or if the animal was imaged on a second day (n = 6). In the oleic acid dogs, the posterior portion of the lung was significantly denser 10 minutes after injection of oleic acid (P less than 0.05), and almost twice as dense 1 hour after initial injection. The density changes determined by CTT in the anterior and posterior lung zones correlated well with the increasing regional wet weight/dry weight relationships determined from the lung on postmortem exam (r = 0.90). We conclude that early subtle density changes in the posterior lung can be found in oleic acid injury pulmonary edema. This can be easily quantitated using CTT, and may prove useful in following physiologic and therapeutic interventions during leaky membrane acute pulmonary injury.