Endometriosis is a common disease in women at reproductive age. We investigated the concentration of neutrophil-activating factor (growth-regulated gene-alpha; GRO-alpha) (a member of the chemokine family), in peritoneal fluid of infertile women with or without endometriosis. Peritoneal fluid was obtained laparoscopically from 22 women with and 21 without visible endometriotic lesions. GRO-alpha concentration was measured by the use of an ELISA kit. Median concentration of GRO-alpha was 87.65 +/- 56.19 pg/ml in the study group and 60.72 +/- 11.98 pg/ml in the control group. The distribution of data differed from normal, therefore logarithmic transformation of data was performed. Concentration of GRO-alpha was significantly higher in the peritoneal fluid of women with endometriosis when compared with controls (p = 0.05). No correlation between concentration of GRO-alpha, stage of endometriosis, duration of infertility or sex steroid hormone levels was found. The study shows that GRO-alpha may play a role in the pathogenesis of endometriosis, possibly by chemoattraction and activation of neutrophils present in higher numbers in the peritoneal fluid of women with endometriosis. It is also feasible that the angiogenic properties of GRO-alpha might prompt the progression of endometriotic lesions.