The role of lead exposure or micronutrient deficiencies in children's sleep problems is unknown. Although elevated blood lead concentrations (BPb) are clearly related to behavior problems in children, few researchers have used objective observations. The authors investigated relationships between lead, micronutrient status, sleep, classroom behavior, and activity in Mexican children aged 6-8 years living close to a metal foundry. Mean BPb was 11.5 +/- 6.1 microg/dL; 50% had levels >or= 10 microg/dL. Ten percent of children had hemoglobin < 12.4 g/dL. Parents reported on children's sleep and fatigue (n 550). The authors also observed classroom behavior (n = 157) and measured physical activity (n = 168). BPb >or= 10 microg/dL was associated with later waking time and shorter duration of sleep. Anemia was linked to more off-task behaviors, lower physical activity, earlier bedtime, and shorter sleep onset. Researchers should investigate these relationships further, using more sensitive measures.