The sulfates of deoxycorticosterone (DOCS), corticosterone (BS), cortisone (ES) and cortisol (FS) were radioimmunoassayed in umbilical vein blood plasma samples collected in 97 fetuses between 19 and 32 weeks of gestation after extraction and chromatography on Sephadex LH 20 columns. While DOCS and BS displayed a decreasing pattern until 27-28 weeks, FS and ES did not show important variations throughout the period considered. All sulfates, excepted BS, increased at 29-30 weeks but this rise was only significant for FS and ES. Thereafter BS significantly increased while no significant difference could be displayed for the three others. In view of the difference between the patterns of 17-deoxy- and 17-hydroxycorticosteroids, one can speculate that, during this period of pregnancy, a shift in steroid biogenesis might occur towards a more important production of cortisol. DOCS was correlated with BS and with FS but not with ES. FS was correlated with the three other sulfates and with unconjugated F. ES was correlated with BS and FS but not with DOCS or unconjugated E. The significance of these correlations are discussed according to the origin and the metabolic interrelationships of the four steroid sulfates and unconjugated F and E.