Hypoxia is one of the commonest causes of perinatal morbidity and mortality. The worst affected are tissues with high oxygen consumption, in particular nervous tissue (Trojan 1978). Criteria enabling prompt and reliable evaluation of the length and intensity of hypoxia are therefore being sought (Saugstad 1975a,b, Tuchschmidt et al .1981, O'Connor et al. 1981a,b). In recent years, conflicting information has appeared in the literature on the possibilities of utilizing the hypoxanthine and xanthine level in body fluids as an indicator of oxygen deficiency (Saugstad 1975a, Tuchschmidt et al. 1981). We therefore tested this criterion in newborn infants at risk from intrauterine hypoxia.