Macrophage-derived substances such as cytokines and growth promoting factors are known to be present in the peritoneal fluid of women with endometriosis. Active endometriosis of the peritoneum is characterised by hypervascularization and neoangiogenesis. TNF-alpha is a pleiotropic cytokine also involved in angiogenesis and immunoregulation. Our question was to determine whether there are differences in the peritoneal TNF-alpha concentrations in women with various degrees of active and inactive endometriosis. We found that TNF-alpha concentrations were higher in the peritoneal fluid of women with endometriosis than in the peritoneal fluid of those without. TNF-alpha concentrations were higher in cases of active endometriosis than in cases of inactive endometriosis. The highest concentrations could be detected in women with severe endometriosis (stage III and IV rAFS).