Thoracic duct drainage (TDD) may be of value for removing toxic substances released by the inflamed pancreas and which are responsible for lung damage. We have prospectively assessed the efficacy of TDD in improving pulmonary gas exchange in 12 patients with severe acute pancreatitis (SAP) complicated by persistent respiratory failure despite standard conservative treatment including peritoneal dialysis in 8 patients. In group A were 6 patients (mean Ranson score = 7.3) with adult respiratory distress syndrome (ARDS) and in group B were 6 hypoxemic patients (mean Ranson score = 6.6) judged to be at risk of developing ARDS. The duration of TDD ranged from 3 to 10 days and the total amount of drained lymph (L) varied from 770 to 15,600 ml. Immunoreactive trypsin levels were significantly higher in L when compared to blood in both groups. Leukocyte myeloperoxidases in L (normal value less than than 332 +/- 82 ng/ml in plasma) were increased in 5 of 5 group A patients (830 +/- 317 ng/ml) and in 3 of 6 patients in group B (671 +/- 467 ng/ml). After TDD pulmonary gas exchange as measured by median PaO2/FiO2 (mmHg) improved from 148 +/- 60 to 285 +/- 42 in group A and from 192 +/- 37 to 330 +/- 42 in group B (p less than 0.05). All patients were weaned after ventilation for a mean of 8 days in group A and 4 days in group B. All patients survived apart from 1 group B patient who died of sepsis on day 34.(ABSTRACT TRUNCATED AT 250 WORDS)