Serum total oestriol concentration was estimated by radioimmunoassay in 370 healthy pregnant women during the 27th and 41st week of gestation. The rise of the serum oestriol was noted from 230,4 +/- 128,2 nmol/L in the 27th week to the peak value of 732,8 +/- 322,4 nmol/L obtained in the 39th week. The changes in the urine total oestrogens measured by immunochemical method were similar but the increase was more uniform and stable. Low correlation (r = 0,25) was found between serum total oestriol and total oestrogens in urine. The results comparison of total oestrogens from urine determined by immunochemical method and obtained by radioimmunoassay has shown excellent and significant accordance (r = 0,98 p less than 0,01).