Two 3-methylcholanthrene inducible cytochromes MC1 (mol. wt. 54500) and MC2 (mol. wt. 57000) were present at very low levels, MC2 mostly in the periportal region but also diffusely distributed throughout the lobule including some centrilobular cells, MC1 concentrated in the centrilobular region. The immunohistological localization of two major groups of glutathione transferases (GST’s) was also different. ‘C’ type proteins (Yb Yb’) and microsomal epoxide hydrolase (EH) , were concentrated around the central vein, whereas the ‘B’ type proteins (Ya Yc) and cytochrome P450 reductase were distributed in a larger area of this region. Thus, the localization was different for some members of the same enzyme family, whilst similarities in the localization existed across the border of the families.