A number of related enzymes like glutathione S-transferases (GSTs) and fatty acid ethyl ester synthases (FAEESs) have been implicated in detoxification and drug resistance. The anionic class of GSTs, π, and closely related FAEES-III exhibit tissue-specific and developmentally regulated expression, and the former has been shown to be overex-pressed or amplified in a variety of tumors. The GSTPl gene has previously been cloned and cytogenetically localized to human 11q13 by in situ hybridization. Using a series of previously described radiation-reduced somatic cell hybrids, we have sublocahzed GSTP1 to 11q13. We isolated a genomic clone containing the entire GSTPl gene and sequenced it. Analysis of the 5’ region revealed 23 (TAAAA) tandem repeats interrupted by a single TA and TAA insertion. This repeat number differs among individuals. Eleven alleles in a mostly Caucasian sample were observed. This repeat has a polymorphism information content of 0.74. Linkage analysis of the Venezuelan reference pedigree places GSTP1 5 cM distal to PYGM and 4 cM proximal to FGF3 thereby providing a genetic marker half-way between these two loci. The sublocalization and genetic characterization of GSTPl facilitates linkage analysis of several disease genes mapped to this chromosome band as well as the correlation of genetic and physical markers in the regi