['To investigate the effects of an aromatase inhibitor, letrozole, on the growth of human endometrium in a three-dimensional fibrin matrix model of endometriosis.', 'Experimental study of human endometrial biopsies in a three-dimensional fibrin matrix culture system.', 'Academic research center.', 'Eight normal women with benign gynecologic problems.', 'Endometrial biopsy samples were washed, cut into small pieces, and placed between two layers of fibrin gel in the presence or absence of letrozole in the culture medium. Tissue changes were assessed by histological and immunohistochemical staining using an inverted microscope, image analysis, and a semiquantitative scoring system.', 'Stromal and epithelial cell outgrowth into the fibrin matrix and angiogenesis comprising endothelial cell invasion of the matrix.', 'Letrozole (0.1 micromol/L, 1 micromol/L, and 10 micromol/L) exerted a significant growth stimulation effect on endometrial tissue in this model.'] Does letrozole stimulate the growth of human endometrial explants cultured in three-dimensional fibrin matrix?