The effect of pregnancy and a chronic, marginal intake of zinc on zinc kinetics was studied in rats. Weanling female rats were fed either a zinc-adequate diet, containing 30 microg Zn/g, (30Zn) (n = 16) or a marginally zinc-deficient diet, containing 6 microg Zn/g, (6Zn) (n = 16). After 6 wk, half of each group was mated (30ZnPG, 6ZnPG). A third group of pregnant rats was pair-fed (PFPG) (n = 6) to the 6ZnPG group. On d 20 of gestation, or at the end of the 9-wk study, 65Zn was injected intravenously. The plasma 65Zn disappearance curve over the next 105 min was used to study the size and fractional turnover rates of two rapidly exchanging zinc metabolic pools (pool a and pool b). Plasma zinc concentrations on d 20 of gestation were significantly lower in the 6ZnPG group compared with the 30ZnPG and PFPG controls, (P < 0.05). The exchangeable pools were also smaller in the 6ZnPG group compared with the 30ZnPg and PFPG groups, (P < 0.02); this reduction was accompanied by a 60% greater fractional turnover rate of pool a, (P < 0.02). Pregnancy outcomes did not differ among the three groups. We conclude that there is an increase in the turnover rate of the exchangeable plasma zinc pool when dietary zinc intake is marginal during pregnancy. This response may help maintain a supply of zinc to the growing fetus when plasma zinc concentrations are reduced.