Our study presents the in vitro molybdenum influence on benzo[a]pyrene (BaP) micro‐somal metabolism. Addition of various concentrations of different molybdenum salts [MoS2, MoCl5, (NH4)6Mo7O244H2O] to liver and lung microsomal fractions of rats previously treated with 3‐methylcholanthrene produces a decrease in the different BaP metabolites assessed by high‐performance liquid chromatography (HPLC) analysis. This inhibition varies, depending on the considered metabolite and in relation to both the molybdenum level and the origin of the microsomal suspension. The minimum effective concentration is 0.26 and 0.52 mM Mo from liver and lung, respectively. The inhibitory potencies of the +5 (chloride) and +6 (ammonium heptamolybdate) molybdenum compounds are comparable; that of the sulfide is lower.