Summary: The possibility of detecting past hypoxia during the first 2 h after birth by means of blood analyses of hypoxanthine, lactate, base deficit, and pH was investigated in six infants with a 1 min Apgar score of ≤4. Reference values for the four biochemical variables were obtained in 16 healthy infants with a normal 1 min Apgar score of ≥8. In the asphyxiated infants, elevated values for hypoxanthine were found in 48%, for lactate in 54%, and for base deficit in 46% while 21% of the pH values were lower than the reference. In the group of asphyxiated infants, significantly elevated hypoxanthine values were found during the first 20 min after birth, base deficit during 30 min, and lactate values during 120 min while lower pH values than the reference were found during the first 30 min. Significant correlations were found between hypoxanthine and lactate concentrations and also between hypoxanthine and base deficit but not between hypoxanthine and pH. It is concluded that the optimal time for detecting past intrauterine hypoxia in the newborn using the hypoxanthine test is between 10 and 20 min after birth, but in individual cases, significantly increased hypoxanthine concentrations may be found at any time in the 10–120 min period. We propose an equation that can be used to calculate an upper normal limit for hypoxanthine concentration in any sampling time during this period.Speculation: The addition of the plasma hypoxanthine concentration to established biochemical tests of perinatal asphyxia such as lactate, base deficit and pH analyses may improve the possibility of detecting past hypoxia accurately. Differences in appearance time, duration and degree of significant changes in the biochemical tests indicates that the optimal sampling time for the disclosure of past asphyxia differs for different tests.