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Summary. A method is described for the isolation of mg quantities of two forms of rat alpha-fetoprotein (AFP) from amniotic fluid by preparative disc-gel column electrophoresis using a continuous elution system. AFP isolated by this method is suitable for use as an antigen, can be labelled for use in a radioimmunoassay and serves as a reference standard. The characteristics of a new antiserum to AFP are also described.The protocol for a radioimmunoassay is outlined which permits the measurement of AFP in several fetal\p=n-\maternalphysiological compartments throughout gestation. Levels of AFP in fetal liver and fetal plasma suggest that secretion of AFP from liver occurs soon after synthesis with minimal hepatic storage. The pattern for AFP in maternal serum parallels that observed in amniotic fluid and fluctuations in maternal serum levels of AFP appear to be buffered by AFP accumulation in amniotic fluid. Fetal clearance of AFP under normal conditions may be relatively constant from Days 11\p=n-\20of gestation since an amniotic fluid : maternal serum AFP ratio of 30:1 is maintained during this period.

Summary Serial measurements of alpha‐fetoprotein (AFP) were made in 63 normal pregnancies throughout gestation using a radioimmunoassay. Significant levels of AFP, which were detected as early as at 10 weeks gestation, showed a gradual rise until 32 weeks, after which the levels declined until term. The limits of the normal gestational pattern have been defined and the intrapatient variability of the assay was examined. A comparison of the clinical characteristics of the pregnancies with levels of AFP was made. Higher birth weights were correlated with later attainment of peak levels of AFP and peak levels were achieved earlier in gestation in female fetuses. Higher levels of AFP and lower oestriol/AFP ratios were correlated with an earlier onset of labour.

L-Phenylalanine: tRNA ligase from E. coli was successfully isolated by affinity chromatography on a column of Sepharose-phenylalanine. The phenylalanine was separated from the Sepharose backbone by two molecules of ε-aminocaproic acid to ensure that there was a minimum of steric interference between the enzyme and the solid matrix.

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