Blood plasma thromboxane-B2 (TXB2) and 6-keto-PGF1 alpha levels were determined by radioimmunoassay technique during the first six to sixteen hours of life in 16 newborn infants with severe asphyxia, 18 newborn infants with mild asphyxia and 27 normal term neonates. Plasma lipid peroxidation (LPO) content was measured by TBA-colour-contrast method in 15 infants with severe asphyxia, 17 infants with mild asphyxia and 24 healthy term newborn infants. The results showed that blood plasma LPO, TXB2 and 6-keto-PGF1 alpha levels in infants suffering from severe asphyxia were higher than those in infants with mild asphyxia and normal infants (P < 0.01), but no significant difference was noted between the mild asphyxia group and normal control group (P > 0.01). These suggest that production of free radicals is increased and prostaglandin metabolism is triggered in the infants with severe asphyxia, that cerebral ischemia and hypoxia caused by asphyxia contributes to the augmented production of prostaglandins and free radicals, and that accumulation of free radicals and prostaglandin enhances brain damage and the metabolism of arachidonic acid appears to be an important source of the free radicals in infants with intrauterine asphyxia.