The purpose of this investigation was to assess the usefulness of maternal and neonatal swine as animal models for studying iron (Fe) and folate nutrition during reproduction and growth. Sows (n = 18) were fed a purified diet containing 0.6 mg folate/kg diet and either 25 (Fe-) or 125 (Fe+) mg iron/kg diet throughout gestation and lactation. Litters were culled to eight on d 2 of lactation and four piglets/litter were given an intramuscular injection of iron dextran (100 mg/kg body wt). Plasma and red blood cell folate concentrations among all sows decreased (greater than 50%) after conception (P less than 0.001). Plasma folate concentration of Fe- sows was 47% and 69% of Fe+ sows on d 7 and 21 of lactation, respectively (P less than 0.05). All sows secreted milk that contained low levels of folate (12-36 nmol/l) and was devoid of long-chain folylpolyglutamates. While mean milk folate concentration significantly decreased after d 1 of lactation among Fe- sows, no such decrease was observed in milk from Fe+ sows (P less than 0.05). Liver folate concentration was significantly reduced in piglets nursed by Fe- sows and given intramuscular iron dextran. It is concluded that there is an increased dietary requirement for folate and iron during reproduction in swine, and that current recommended amounts of folate (0.6 mg/kg diet) and iron (80 mg/kg diet) may be underestimates of requirements for reproduction. Further, results show that iron nutrition may alter folate utilization in maternal and neonatal swine.