There is a concern that exclusive breast-feeding (EBF) for 6 mo may lead to iron and zinc deficiency in low-birth weight (LBW) infants. We assessed the association between duration of EBF and infant iron and zinc status in the Maternal and Infant Nutrition Interventions in Matlab trial, Bangladesh, stratified for normal birth weigh (NBW) and LBW. Duration of EBF was classified into EBF <4 mo and EBF 4-6 mo based on monthly recalls of foods introduced to the infant. Blood samples collected at 6 mo were analyzed for plasma zinc (n = 1032), plasma ferritin (n = 1040), and hemoglobin (Hb) (n = 791). Infants EBF 4-6 mo had a higher mean plasma zinc concentration (9.9 +/- 2.3 micromol/L) than infants EBF <4mo (9.5 +/- 2.0 micromol/L) (P < 0.01). This association was apparent in only the NBW strata and was not reflected in a lower prevalence of zinc deficiency. Duration of EBF was not associated with concentration of plasma ferritin, Hb concentration, or prevalence of iron deficiency or anemia in any strata. Regardless of EBF duration, the prevalence of zinc deficiency, iron deficiency, and anemia was high in infants in this population and strategies to prevent deficiency are needed.