The five stable metabolites [prostaglandin F2 alpha, prostaglandin D2, prostaglandin E2 (PGE2), thromboxane B2, and 6-keto-prostaglandin F1 alpha] of arachidonic acid (AA) via the cyclooxygenase pathway were measured by high-resolution gas chromatography-mass spectrometry in Lewis lung carcinoma homogenates at various times after tumor implantation (11 to 25 days). Vegetating and necrotic sections of the primary tumor and lung metastases were examined. Vegetating tumor showed a very active AA metabolism. Synthesis of PGE2, the most abundant product, markedly increased during tumor growth (up to 30 micrograms/g). A high and increasing synthetic capacity was also noted for prostaglandin D2 (up to 9 micrograms/g). Minor time differences and lower levels (up to 1.4 micrograms/g) were found for the other AA metabolites. PGE2 and prostaglandin D2 were the major products in necrotic tumor, too, but synthesis was markedly less than in vegetating tumor, and no increase was noted over time. Metastatic tissue showed a different AA metabolic profile, as compared to primary tumor and surrounding lung tissue, with PGE2 and 6-keto-prostaglandin F1 alpha being the main metabolites.