OBJECTIVE: The aim of this work was to establish reference values for methemoglobin levels in 6 to 10-year-old children. METHODS: Methemoglobin concentrations were studied in clinically healthy children. The method for methemoglobin measurement used, neither uses highly toxic chemical compounds nor expensive enzymatic methods, thus it is feasible in the laboratory routine. RESULTS: The results showed higher reference values for clinically healthy children (from 3.61 to 6.44%) than for adults (from 1.9 to 3.8%). CONCLUSIONS: The higher concentrations of methemoglobin in children may be explained by smaller amounts of soluble cofactor cytochrome b5 and reduced activity of the cytochrome b5 reductase enzyme in red blood cells which make children particularly susceptible to the development of methemoglobinemia. Methemoglobin concentrations in children are higher than in normal adult subjects thus, adult reference values cannot be used to interpret infant methemoglobinemia.