Radioimmunological assay of alpha-fetoprotein (AFP) has been performed in the serum of normal women at various stages of pregnancy and at the time of parturition; a total of 208 assay was carried out, AFP values rose until the 33rd week and at the time of childbirth dropped to levels about half of the maximum reached. No correlations were found between AFP values, neonatal weight and parity while the sex of the fetus appearech to have some influence. It is to be hoped that the application of these potential uses can be envisaged in the near future.