Six patients each with a very low 24-hour urine oestriol excretion were infused with hypertonic dextrose and amino acids for 48 hours prior to delivery. Amniotic fluid samples were studied before and after infusion. Lecithin sphingomyelin ratios and insulin levels were increased following infusions in all patients. There was usually a fall in amniotic fluid glucose and an increase in ammonia, amino acid nitrogen and osmolality following infusions. Maternal plasma oestriol, human placental lactogen, cystyl aminopeptidase and urine oestriol excretion were unchanged during the infusions.