Forty-nine outpatients with precordial pains were studied by the treadmill exercise test. Before, immediately after and 30 minutes after exercise, blood samples were obtained from antecubital veins, measuring plasma TXB₂, 6-keto PGF_1α, cyclic AMP and cyclic GMP levels by radioimmunoassay. The results of exercise tests were evaluated with the treadmill exercise score (TES) by Hollenberg et al, by which the patients were divided into two groups, TES (-) with ischemic findings in exercise and TES (+) with normal exercise. Changes of plasma prostanoids and cyclic nucleotides in each group were analyzed. There were no differences in TXB₂ levels between two groups before exercise. Immediately after exercise statistically significant difference of TXB₂ levels were present between two groups, resulting from the increased levels in TES (-) group and decreased in TES (+) group (p<0.01). Although 6-keto PGF_1α levels also showed no differences between two groups before exercise, 6-keto PGF_1α levels in TES (+) group were increased statistically significantly immediately after exercise. In consequence statistically significant differences (p<0.01) were observed between two groups and between the levels before exercise and immediately after exercise in TES (-) group. Similar changes were present in cyclic nucleotiedes, especially cAMP levels before exercise between two groups (p<0.05) and their differences increased more immediately after exercise (p<0.01). In ischemic heart disease, prostaglandins might play an important roles, especially the failure of PGI₂ production to counteract to the increase of TXA₂ by exercise may be an important phenomena to know the physiological conditions of ischemic heart disease.