Endometriosis is an important contributing factor to chronic pelvic pain and infertility. Matrix metalloproteinases (MMPs) and vascular endothelial growth factor (VEGF) have each been implicated in the establishment of endometriotic lesions. Since relaxin regulates the expression of MMPs and VEGF in the endometrium, we tested the hypothesis that relaxin plays a role in endometriosis by comparing the expression of relaxin mRNA and its LGR7 (RXFP1) receptor mRNA in normal human endometrium to those in samples from patients with endometriosis.