The aim of this study was to determine whether blood gas variables in fetal capillary blood during the last 30 min of stage II labor can be used to diagnose fetal asphyxia. Twenty-five newborn calves were used to investigate the correlation between capillary blood gas values obtained from the dorsolateral aspect of the distal pastern and those in arterial and venous blood. The pH, partial pressure of oxygen, partial pressure of carbon dioxide, concentration of bicarbonate, base excess and oxygen saturation were determined. The bicarbonate concentration (arterial, r=0.759; venous, r=0.766; both P<0.0001) and base excess (arterial, r=0.730; venous, r=0.807; both P<0.0001) had the highest correlations. Fetal capillary blood was collected during the last 30 min of stage II labor and the results of blood gas analysis were compared with those of arterial and venous blood collected immediately after birth in 38 calves. The pH (arterial, r=0.806; venous, r=0.885; both P<0.0001) and base excess (arterial, r=0.822; venous, r=0.871; both P<0.0001) had the highest correlations. The pH and base excess were significantly lower after birth than during the last 30 min of stage II labor. The severity of fetal acidosis during stage II labor can be easily and reliably determined using the pH or base excess of fetal capillary blood.