The influence of dietary nicotinamide deficiency on lead intoxication in young developing rats was investigated. The Pb induced an increase in brain dopamine and noradrenaline, inhibition in blood δ-aminolevulinic acid dehydratase activity, an elevation in urinary excretion of δ-aminolevulinic acid and blood and tissue uptake of Pb were significantly more marked in animals maintained on a nicotinamide-deficient diet than those fed a nicotinamide-sufficient diet. The nicotinamide deficiency may enhance the susceptibility to Pb intoxication possible by enhancing the absorption of Pb and altering nicotinic acid metabolism.