The majority of studies published so far consistently support the above-mentioned dependencies by indicating the greater expression of the following MMPs or their mRNA as measured in the eutopic and ectopic endometrium, serum, or follicular fluid of patients with endometriosis compared to healthy women: MMP-2 [90,91] and MMP-9 [91,92]; moreover, the positive relationship between MMP concentrations and the severity of endometriosis was also suggested [93]. Here, MMP9 is linked to endometriosis.