Serum levels of tryptophan (Trp) and 5-hydroxytryptophan (5-HTP) were measured in the mother at birth, by normal delivery or cesarean section, on days 1 and 3 post-partum, and in the cord blood of the fetus-newborns. Decreases in Trp and 5-HTP levels during delivery were noted. Conversely, Trp levels in the cord blood of fetus-newborns were significantly higher than those of their mothers, and 5-HTP levels also showed a tendency to increase , whereas on day 1 post-partum Trp values were lower than those in fetal cord, but higher than those during spontaneous delivery. On day 3 post-partum, serum Trp levels were higher than those during spontaneous delivery, but similar to those on day 1. 5-HTP values tended to decrease with respect to those of day 1. Serum Trp and 5-HTP concentrations decreased significantly on day 1 post-partum after cesarean section, but increased on day 3, demonstrating that maternal Trp was being consumed during delivery. A major release of prolactin in serum on days 1 and 3 post-partum there was in women with normal delivery, revealing a correlation between Trp and prolactin in the first few days after birth, in relation to different conditions of delivery.