The possibility that Pb could affect benzene metabolism, through inhibition of enzyme synthesis, was examined by studies of the effects of chronic oral Pb treatments on benzene conversion to phenol. Rats were given either distilled delonized water or 0.05, 0.58, 17, or 352 ppm Pb solutions as drinking water. After 6, 9, 12, and 75 wk of treatment, rats from each group were sacrificed andin vitrobenzene metabolism by benzene hydroxylase was measured in liver enzyme preparations. After 24 wk, the remaining animals were injected ip with 400 mg/kg benzene and urinary phenol levels measured daily for 4 d.