To assess the value of cord plasma arginine vasopressin (AVP), erythropoietin (EP), and hypoxanthine (HX) as indices of asphyxia, we studied 62 infants of mothers with preeclampsia, 34 acutely asphyxiated infants, with 5-min Apgar score less than or equal to 6 and/or umbilical arterial pH less than or equal to 7.05, and 38 control infants. Umbilical arterial AVP in the asphyxia group (geometric mean; 95% confidence interval: 180; 92-350 pg/ml) was higher than in the control group (23; 8-66, p = 0.002) and correlated with umbilical arterial pH (r = -0.447, p = 0.028). AVP levels in the preeclampsia group did not differ from controls. Cord venous EP was higher in infants delivered by elective cesarean section from women with severe preeclampsia (115; 75-177 mU/ml, p less than 0.001) than in control infants (23; 18-27); in the whole group EP correlated with pH (r = -0.493, p less than 0.001). EP in the asphyxia group was similar (46; 35-65) to controls (40; 33-47) and did not correlate with pH. Cord arterial HX in the preeclampsia group was similar to controls (12.3; 9.5-16.0 mumol/liter), but elevated in the asphyxia group (23.7; 17.6-31.8, p = 0.001), in which HX correlated with pH (r = 0.558, p = 0.008) and AVP (r = 0.588, p = 0.005). EP did not correlate with AVP or HX in any group, nor did any of the variables correlate with the Apgar score. We conclude that cord plasma AVP and HX reflect acute asphyxia, whereas EP is elevated after more prolonged hypoxia.