The role of prostaglandins in endocrine diarrheagenic syndromes was evaluated by measuring peripheral concentration of immunoreactive PGE and PGF in patients with non-endocrine diarrhea as well as those with the Zollinger-Ellison (Z-E) syndrome, MCT, carcinoid tumors and the WDHA syndrome. In 21 normals, PGE and PGF levels averaged 272 +/- 18 and 119 +/- 14 pg/ml, respectively. Twenty eight patients with diarrhea of non-endocrine origin (mainly inflammatory bowel disease) had levels indistinguishable from normal, i.e. 353 +/- 25 and 77 +/- 37 pg/ml, respectively. Among 29 patients with the Zollinger-Ellison syndrome (mean gastrin 6127 +/- 3267 pg/ml) only 2 had significantly elevated PGE levels; mean PGE levels, 382 +/- 32 pg/ml, were not significantly different from normal and did not correlate with either diarrhea or the serum gastrin concentration. In contrast, 18 of 22 patients with carcinoid tumors (mean blood serotonin concentration 1655 +/- 604 ng/ml; mean urinary excretion of 5 HIAA 66.8 +/- 16.7 mg/day) had elevated peripheral concentrations of PGE. The mean PGE level (1367 +/- 245 pg/ml) was significantly elevated (P less than 0.001). Nonetheless PGE levels did not correlate with diarrhea, blood concentrations of serotonin, or urinary indole excretion. MCT (mean serum calcitonin 24.5 +/- 6.3 ng/ml) was similarly associated with consistent (18/19) elevation in peripheral concentrations of PGE (mean 1922 +/- 541 pg/ml; P less than 0.001). Inthis syndrome, PGE levels were higher in patients with diarrhea and in those with markedly elevated serum thyrocalcitonin levels. Finally, 8 of 21 patients with the WDHA syndrome had increased levels of PGE. Although 13 of 17 patients had high levels of VIP (mean 8133 pg/ml), 2 patients had hyperprostaglandinemia in the face of normal peripheral concentrations of VIP. In one patient the serum PGE level was elevated prior to resection of the primary pancreatic neoplasm (9939 pg/ml) as well as the subsequent extirpation of a solitary hepatic metastasis (1063 pg/ml); following each procedure the diarrhea abated and the PGE level returned to normal. In none of these syndromes were mean PGF levels elevated. The study has documented hyperprostaglandinemia in some endocrine diarrheagenic syndromes and validated the usefullness of measurements of PGE in patients with unexplained diarrhea.