There were no significant differences in the HYAL2 mRNA or protein expression in endometrial epithelial cells (EECs) or stromal cells (ESCs) with and without endometriosis [89], nor in the 4-methylumbelliferone (4-MU)–hyaluronic acid synthesis inhibitors, the expression of the hyaluronic acid (HA) system, or the inhibition of hyaluronidase by endometrial epithelial cells (EECs) or stromal cells (ESCs) on peritoneal mesoepithelial cells (PMCs). The gene discussed is HYAL2; the disease is endometriosis.