Intratumoral biosynthesis of hormone steroids is thought to play a role in the pathogenesis and development of human breast cancer. There is evidence that glucocorticoids may inhibit the development and progression of breast cancer. 11β-hydroxysteroid dehydrogenase (11β-HSD) type 1 is the enzyme which converts inactive cortisone to active cortisol. In order to study the expression of 11β-HSD type 1 in breast cancer and non-cancerous breast tissue, we have developed specific antibodies to 11β-HSD type 1 and proceeded to localization of the enzyme in 84 specimens of breast carcinoma and adjacent non-malignant tissues by immnohistochemistry. The results were correlated with the expression of androgen receptor, estrogen receptor, progesterone receptor, glucocorticoid receptor and CDC47, a cell division marker, as well as the tumor stage, tumor size, nodal status and menopausal status. The expression of 11β-HSD type 1 in 64% of breast cancer specimens appeared significantly lower than that observed in normal adjacent tissues (97% of cases being positive). There was no significant correlation between 11β-HSD type 1 expression and the clinicopathological parameters studied. The decrease in 11β-HSD type 1 expression in breast cancer as compared to that observed in the adjacent normal tissues may play a role in the development and/or progression of the cancer by modifying the intratumoral levels of glucocorticoids.