Endometriosis is characterized by the implant growth and development of endometrial tissue in an extrauterine location. Approximately 5—15% of women present the disease during the reproductive years. Various immunological alterations could explain the development of endometriosis. Those most studied include: an increase in the number and cytotoxicity of macrophages in the peritoneal liquid; polyclonal increase in the activity of B lymphocytes; abnormalities in the functions and concentrations of B and T lymphocytes; and reduction in number or the activity of the natural killer cell. Furthermore involvement of the humoral immune response in endometriosis with the production of anti-endometrium antibodies has already been described. (excerpt)