Eker rats carry a defect in the Tsc-2 tumor suppressor gene and female Eker rats develop uterine leiomyoma with a high frequency. The presentation, response to hormones and molecular alterations in these mesenchymal smooth muscle tumors, closely resembles their cognate human disease. Female rats and tumor-derived cell lines from Eker rat leiomyomas (ELT lines) have been developed as an in vivo/in vitro model system for preclinical studies to identify novel therapeutic agents for this disease and for studying disease pathogenesis. In addition to serving as a model for uterine leiomyoma, Eker rats have proven valuable for studying lymphangioleiomyomatosis, a related proliferative smooth muscle disease of women. Copyright 2003 Wiley-Liss, Inc.