Several products of arachidonic acid metabolism were assayed in whole saliva of patients with cystic fibrosis, a disease affecting primarily the exocrine glands. The levels of prostaglandins (PG) E2 and F2 alpha were elevated fourfold in patients with cystic fibrosis, compared with a control group (mean +/- SEM for PGE2 1.13 +/- 0.22 vs 0.37 +/- 0.08 ng/ml saliva, p less than 0.005; and for PGE2 alpha 0.84 +/- 0.27 vs 0.17 +/- 0.03 ng/ml saliva, p less than 0.025). The levels of PGI2, hydroxyeicosatetraenoic acids, and leukotrienes showed no significant differences between the two groups. These changes were not present in individuals heterozygous for the cystic fibrosis gene. Study of appropriate control groups suggested that the changes that we observed in patients with cystic fibrosis could not be attributed to their lung disease or to the medications these patients were receiving. Our findings indicate that metabolism of arachidonic acid is abnormal in cystic fibrosis.