Matrix metalloproteinases (MMP) are strongly implicated in menstruation. Messenger RNA for proMMP-1 and -3 was detectable in normal cycle endometrium only peri-menstrually and menstrually, although mRNA for their tissue inhibitors, TIMP-1 and TIMP-2, was present throughout the cycle. MMP-1, -3 and -9 were demonstrated immunohistochemically to be specifically associated with degraded tissue in m...