Concentrations of FAldo and GAldo were simultaneously measured by specific RIA in 84 samples of human amniotic fluid (AF)collected between 15-34 weeks in normal pregnancies. PAldo was concomitantly determined by RIA on samples obtained at 14.00 hr, after two hours decubitus. PAldo showed a significant rise during pregnancy, its level averaging 134.5 ± 10.8 pg/ml (mean ± SEM) before 20 weeks (n = 62) and 288.2 ± 49.2 pg/ml between 20-34 weeks (n=22) {p < 0.01). In AF, the increase of GAldo during the second stage of pregnancy largely exceeded that of FAldo rising from 81.2 ± 5.7 pg/ml to 269.5 ±61.2 pg/ml and from 84.0 ±5.9 pg/ml to 118.8 ± 11.5 pg/ml for the latter between the 15-20 weeks and 20-34 weeks periods. A significant relationship between AF levels and age of pregnancy could only be detected for GAldo (r= 0.691, p<0.01). Our results agree with patterns of PAldo (Weir et al, 1974, Ledoux et al, 1975) and FAldo (Blankstein et al, 1980, Sippell et al, 1981) already reported. The increase of GAldo presently described disagrees with its high and stable level reported by Aderjan et al (1977) on poorly documented data. Simultaneous determination of F- and G-Aldo shows that the rate of increase of fetal aldosterone production is higher than could be expected from estimation of FAldo alone. Augmentation of GAldo in AF probably expresses both the increased contribution of urine to AF and the maturation of renal glycuronoconjugation process.