Carcinogenic activity of many polycyclic aromatic hydrocarbons (PAHs) is mainly attributed to their respective diol epoxides, which can be classified as either bay or fjord region depending upon the location of the epoxide function. The Pi class human glutathione (GSH) transferase (hGSTP1-1), which is polymorphic in humans with respect to amino acid residues in positions 104 (isoleucine or valine) and/or 113 (alanine or valine), plays an important role in the detoxification of PAH-diol epoxides. Here, we report that the location of the epoxide function determines specificity of allelic variants of hGSTP1-1 toward racemic anti-diol epoxide isomers of benzo[c]chrysene (B[c]C). The catalytic efficiency (k(cat)/K(m)) of V104,A113 (VA) and V104,V113 (VV) variants of hGSTP1-1 was approximately 2.3- and 1.7-fold higher, respectively, than that of the I104,A113 (IA) isoform toward bay region isomer (+/-)-anti-B[c]C-1,2-diol-3,4-epoxide. On the other hand, the IA variant was approximately 1.6- and 3.5-fold more efficient than VA and VV isoforms, respectively, in catalyzing the GSH conjugation of fjord region isomer (+/-)-anti-B[c]C-9,10-diol-11,12-epoxide. The results of the present study clearly indicate that the location of the epoxide function determines specificity of the allelic variants of hGSTP1-1 in the GSH conjugation of activated diol epoxide isomers of B[c]C.