The perioperative behaviour of PGE2 and DHK-PGF2 alpha was studied in peripheral blood of patients undergoing lung surgery. The measurement of prostaglandins was performed by RIA after an extraction procedure. Common control criteria were observed. In 39 patients blood sampling was performed preoperatively and 2 weeks postoperatively. PGE2 and DHK-PGF2 alpha were significantly elevated in 8 patients with lung cancer before the operation. Postoperatively the concentrations decreased; 2 weeks later, DHK-PGF2 alpha was still slightly increased, PGE2 had normalized. 9 patients suffering from tuberculosis had normal serum concentrations of PGE2 and DHK-PGF2 alpha before and after resection procedures. In 8 cases the resection of benign lung diseases did not cause any abnormal reactions. In 2 special groups blood sampling was performed the following way: in 4 cancer patients and 3 tuberculosis patients blood was collected preoperatively, 5 times in the first hour after lung resection and 1 day and 2 weeks after operation. It could be demonstrated that PGE2 and DHK-PGF2 alpha almost completely normalized within the first postoperative hour in cancer patients, whereas no significant alterations could be found in tuberculosis. After discussion of technical problems in the measurement of prostaglandins the alterations of PG concentrations after lung cancer resection are emphasized.