Ellagic acid (EA), a plant phenol found in a variety of fruits and vegetables normally consumed by humans, inhibited the metabolism of benzo[a]pyrene (B[a]P) and covalent binding of B[a]P metabolites to DNA in cultured lung explants from strain A/J mice. Explants were incubated in medium containing EA at concentrations of 10 - 100 microM for 16 h followed by the addition of 1 microM [3H]B[a]P for 24 h. Culture medium was extracted and analyzed by high-performance liquid chromatography. DNA from the explants was extracted, purified and quantitated to determine B[a]P metabolite binding to DNA. EA at concentrations of 10, 25, 50, 100 microM inhibited the metabolism of B[a]P in lung explants by 24-47% and DNA-binding of B[a] metabolites by 36-71%. Analysis of total lipids and trichloroacetic acid insoluble fractions of homogenized lung explants showed two to three times more radioactivity in EA-treated cultures even though EA did not affect the uptake of B[a]P. Explants maintained for four days after the removal of EA and [3H]B[a]P from the culture medium exhibited significant persistence of B[a]P and B[a]P metabolites associated with the total lipid and TCA insoluble fractions and in B[a]P metabolites bound to DNA. H.p.l.c. analysis of the total lipids extracted from homogenized lung explants showed that during the first 3 days of incubation most of the radioactivity in the EA-treated cultures was unmetabolized B[a]P while that in the control cultures existed as metabolites of B[a]P. The inhibition of metabolism of B[a]P and the consistently lower B[a]P-DNA binding in EA-treated mouse lung explants support the role of EA as a naturally occurring inhibitor of B[a]P-induced carcinogenesis.