The human estradiol 17 beta-hydroxysteroid dehydrogenase II (17 beta-HSD II) gene has been assigned by somatic cell hybridization to chromosome 17q11-q21, near the region of assignment of the gene BRCA1, which is involved in hereditary breast-ovarian cancer. The nucleotide sequence of 17 beta-HSD II was completely determined in four unrelated individuals. Direct sequencing of PCR fragments that span the complete 17 beta-HSD II gene revealed a total of 11 allelic variants which were due to single base substitutions. The presence of these variants was then studied in twenty six additional unrelated individuals. There were nine frequent and two rare polymorphisms. Seven of the 11 polymorphisms were in complete linkage disequilibrium. These polymorphisms in the 17 beta-HSD II gene provide markers that can be used for the genetic mapping of this locus, and may be used to establish whether 17 beta-HSD II is a candidate gene for hereditary breast-ovarian cancer.