6 beta-Hydroxycortisol (6 beta OHF) is a highly polar metabolite of cortisol, probably formed in the endoplasmic reticulum of hepatocytes by cytochrome P-450-dependent microsomal monoxygenases. Lead decreases the activity of cytochrome P-450-dependent microsomal hydroxylases in vivo and in vitro. To examine possible inhibitory effects of lead on 6 beta OHF metabolism, urinary 6 beta OHF excretion was measured in 26 children with mild to moderate increases in blood lead concentrations. Children were divided into 2 groups on the basis of their response to the EDTA provocative test. This test was used to assess the size of chelatable and potentially toxic lead stores in such children. Children with elevated urinary lead excretion after an EDTA provocative test, i.e. elevated tissue lead stores, had markedly decreased urinary excretion of 6 beta OHF (178 +/- 15 micrograms/m2 X 24 h) compared to children who had negative tests (333 +/- 40 micrograms/m2 X 24 h; P less than 0.01); their urinary cortisol excretion was not different from that of age-matched controls. These findings suggest that lead, at relatively low concentrations, may interfere with hepatic microsomal formation of a cortisol metabolite.