Molybdenum (Mo), selenium (Se) and copper (Cu) plasma levels were studied at delivery in 38 women (1 twin pregnancy). The influence of parity (P) (2.5 +/- 1.7) gestational age (GA) (38.6 +/- 3.2 weeks), birthweight (BW) (3,120 +/- 695 g) and Apgar score upon these levels were assessed. Mother (M) and cord (C) blood values were 15.0 +/- 7.8 and 15.0 +/- 9.3 nmol/l respectively for Mo, 0.54 +/- 0.12 and 0.47 +/- 014 mumol/l for Se and 27.6 +/- 5.9 and 5.5 +/- 3.3 mumol/l for Cu. C and M values for Se and Cu were statistically different (alpha less than 0.02, alpha less than 0.001). There was a significant correlation between C and M for Mo levels (r = 0.41; p = 1.9%) and Cu levels (r = 0.47; p = 0.35%), between Cu C levels and GA (r = 0.54; p = 0.6%) and between Se, C levels and BW (r = 0.66; p = 1.9%). There was no correlation between the levels of the trace elements studied. This study shows that fetal levels of Mo vary with those of the mothers. On the other hand, the levels of Se in the fetus seem to be protected from variations observed in the mothers. The antagonism between Cu and Mo which had been previously demonstrated in the fetal liver was not found in blood.