To evaluate erythropoietin (Ep) levels in normal labor and cesarean section we studied the cord serum of 111 term pregnancies, divided into three groups: (i) those born by normal vaginal delivery (n = 69); (ii) those delivered vaginally from mothers who were smokers (n = 20); and (iii) those delivered by elective cesarean section (n = 22). The three groups did not differ in maternal age, gestational age, birthweight, infant sex and Apgar scores. No correlation was found between Ep and hematocrit in all three groups of normal terms studied. Although not statistically significant the lower mean Ep value observed in cesarean section compared with the values obtained from normal deliveries could suggest that the process of labor may be a cause of these differences.