A highly sensitive radioimmunoassay for the gonadotropin releasing hormone has been developed in order to study its physiological importance in man. In view of the expected low concentrations in peripheral blood, large volumes of human plasma were extracted by two different methods and characteristics of the radioimmunoassayable material compared with those of synthetic decapeptide and extracts of human hypothalami. The results indicate that radioimmunoassayable gonadotropin releasing hormone is present in some human plasmas but the plasma concentration are less than 2.5 pg/ml. Peripheral levels were more consistently measurable in women at midcycle and after the menopause. The hormone was undetectable in the plasma of normel men, human cerebrospinal fluid, and fetal cerebral tissue, but was present in fetal hypothalami.

Because respiratory distress syndrome (RDS) may occur in one twin but not the other it may be misleading to assess fetal lung maturity using amniotic fluid from only one sac. We compared the amniotic fluid lecithin/sphingomyelin (L/S), phosphatidyl glycerol/sphingomyelin (PG/S) and phosphatidyl inositol/sphingomyelin (PI/S) ratios between cotwins and co-triplets in 32 sets of twins and three set of triplets. In the twin pregnancies we found a weak correlation for L/S ratio but a much improved one for PG/S and PI/S. The concordance between sacs for all three ratios was better in monozygotic than in dizygotic twins. The efficacy of amniotic fluid PG in the determination of fetal lung maturity was demonstrated and the discrepancies between the sacs was much less for

Summary. Immunoreactive LH-RH was present in all the hypothalamic and cortical extracts of mid-term human fetuses studied and in the cortical tissue removed from the two youngest fetuses. Gonadotrophin-releasing activity of hypothalamic and cortical extracts was demonstrated by the significant rises of circulating LH after infusion into oestrogen and progesterone-primed ovariectomized rats.

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In spite of major improvements in neonatal intensive care, mortality and morbidity remain a problem for the very preterm baby. In a study of 168 babies born before 36 weeks the presence of phosphatidylglycerol (PG) as a marker of fetal lung maturity in amniotic fluid or pharyngeal aspirate was associated with a lower requirement for ventilatory support and a reduced incidence of intraventricular haemorrhage and patent ductus arteriosus. It is suggested that the value of the antenatal assessment of fetal lung maturity should Perhaps be reviewed since babies in whom PG is absent appear to be at a high risk of sustaining considerable morbidity.