Résumé : Levels of human chorionic gonadotrophin (hCG) and of its free a and p subunits were measured using specific immunoradiometric assays in exocoelomic fluid (ECF) and maternal serum (MS) collected from five pregnant women at 6.6-8 weeks of gestation. Mean levels of hCG and its free subunits were significantly (P<0.001) higher in ECF than in MS: 3.5-fold for hCG, 600-fold for free αhCG and 38-fold for βhCG. There was no correlation between either hCG levels or levels of its free subunits in ECF and MS. On a molar basis, the quantity of free αhCG subunit expressed as a percentage of the total (free+combined) amount was 83% in ECF and 2.7% in MS (P<0.001). The amount of free βhCG subunit as a percentage of the total was 22% in ECF and 3.5% in MS (P<0.001). The ratio of the total amounts of α- and βhCG subunits amounted to 4.6 in ECF and 0.99 in MS (P<0.001). The heterogeneity of hCG was further investigated by polyacrylamide gel electrophoresis followed by immunoblotting. Several bands with molecular mass ranging from 42 to 57kDa, corresponding to hCG dimers, were immunodetected in ECF and MS with anti-αhCG and anti-αhCG monoclonal antibodies. A free 35 kDa βhCG immunoreactive band was found in ECF and MS. A free αhCG immunoreactive band was observed at 23 kDa in ECF and at 21 kDa in MS. These findings suggest that the exocoelomic cavity is a reservoir where hCG and its subunits produced by trophoblast accumulate directly. The excess of a free heavy αhCG subunit in ECF supports the hypothesis that, during early pregnancy, there is an excess of αhCG over βhCG subunit secretion by the trophoblast.