1. Distribution of zinc between the metalloprotein α2-macroglobulin and albumin was determined in samples of serum obtained from twenty-three women in their third trimester of pregnancy and eighteen women who were not pregnant.
2. The decrease observed in total serum zinc in the group of pregnant women could be accounted for in large part by a decreased concentration of albumin-bound zinc.
3. The concentration of serum albumin was lower in the pregnant women, thus hypoalbuminaemia, which is often invoked to explain hypozincaemia in pathological situations, may in part account for hypozincaemia in pregnancy.
4. The affinity of albumin for zinc added to serum from pregnant women was less than that of albumin from non-pregnant women. This was determined by competition experiments between albumin and glycine for zinc. Decreased affinity of serum albumin for zinc may also contribute to the hypozincaemia associated with pregnancy.