The study objective was to determine whether stromal and/or epithelial estrogen receptor-α(ERα) is required for relaxin to promote proliferation of stromal and epithelial cells in the mouse cervix. Four types of tissue recombinants were prepared with cervical stroma (St) and epithelium (Ep) from wild-type (wt) and ERα knockout (ko) mice: wt-St+wt-Ep, wt-St+ko-Ep, ko-St+wt-Ep and ko-St+ko-Ep. Tissue recombinants were grafted under the renal capsule of syngeneic female mice. After 3 wk of transplant growth, hosts were ovariectomized and fitted with silicon implants containing 17β-estradiol (treatment d 1). Animals were injected sc with relaxin or vehicle PBS at 6-h intervals from 0600 h on d 8 through 0600 h on d 10. To evaluate cell proliferation, 5-bromo-2́-deoxyuridine was injected sc 10 h before tissue recombinants were collected at 1000 h on d 10. Relaxin promoted marked proliferation of both epithelial and stromal cells in tissue recombinants containing wt St (P < 0.001) but far lower proliferation in recombinants prepared with ko St, regardless of whether Ep was derived from wt or ko mice. An additional experiment using mice expressing wt ERα, a mutant of ERα that selectively lacks classical signaling through estrogen response element binding, or no ERα demonstrated that ERα must bind to an estrogen response element to enable relaxin's proliferative effects. In conclusion, this study shows that ERα-expressing cells in St, using a classical signaling pathway, are necessary for relaxin to promote marked proliferation in both stromal and epithelial cells of the mouse cervix. Copyright © 2010 by The Endocrine Society.