Excretion of 2,3-dinor-6-ketoprostaglandin F1 alpha and 2,3-dinorthromboxane B2, the main urinary metabolites of prostacyclin and thromboxane, was evaluated by gas chromatography-mass spectroscopy and radioimmunoassay, respectively, at various conditions in man. In healthy young males excretion of 2,3-dinor-6-ketoprostaglandin F1 alpha was of little variability, whereas urinary 2,3-dinorthromboxane B2 showed marked interindividual but moderate intraindividual variations. The ratio of urinary 2,3-dinorthromboxane B2 to thromboxane B2 in young males was about 15. Excretion of 2,3-dinor-6-ketoprostaglandin F1 alpha in women of reproductive age was higher (155 +/- 23 ng/g creatinine, P less than 0.005) than in postmenopausal women (97 +/- 24 ng/g creatinine) and in men (78 +/- 7.6 ng/g creatinine) and increased significantly during pregnancy (1st trimester 230 +/- 50 ng/g creatinine; 3rd trimester 522 +/- 53 ng/g creatinine). Urinary 2,3-dinorthromboxane B2 showed no gender differences and no directed change was observed during pregnancy. In neonates urinary 2,3-dinorthromboxane B2 (6.328 +/- 1.210 ng/g creatinine) was high in their 3rd day of life and decreased rapidly thereafter. This pattern paralleled the behavior of 6-ketoprostaglandin F1 alpha. In young male smokers and non-smokers excretion of 2,3-dinor-6-ketoprostaglandin F1 alpha was not significantly different, whereas urinary 2,3-dinorthromboxane B2 was elevated in smokers (609 +/- 61 versus 351 +/- 41 ng/g creatinine, P less than 0.001). Values are mean +/- S.E.