Low levels of blood ascorbate in pregnant women had been thought to have a role in incidence of premature rupture of membranes (PROM). In this study, maternal and fetal blood levels of ascorbate were surveyed in term and preterm labor. Each group was subdivided according to the presence of PROM. Placental ascorbate levels were also studied. Since ascorbate is known to be involved in the synthesis of collagen, hydroxyproline content of the amnion was also measured and taken as an index for collagen production. Amnionic membranes from births with PROM showed relatively low levels of hydroxyproline. Preterm newborns with PROM also exhibited a significantly low ascorbate concentration as compared with preterm controls. In conclusion, ascorbate in the fetal compartment appears to be important for the occurrence of PROM.