Endometriosis is a chronic gynecological disorder defined as the presence of endometrial tissue within extra-uterine sites. The primary symptoms are infertility and chronic pain. The inflammatory environment and aberrant immune responses in women with endometriosis may be directly associated with the initiation and progression of endometriotic lesions. In the present study, the secretion of inflammatory cytokines was evaluated in cultures of primary endometrial cells (ECs) isolated from the endometrium of women with and without endometriosis. The presence of endometriotic cells leads to alterations in the secretory profile of healthy ECs. The expression of the inflammatory cytokines interleukin (IL)‑6 and IL‑8 was significantly increased in endometriotic and co‑cultured cells compared with healthy ECs. IL‑6 expression was strongly correlated with IL‑8 expression in endometriotic cells. IL‑1β expression was increased on day 10 of co‑culture to 48.30 pg/ml and may be associated with the long‑term co‑culture, rather than IL‑6 and IL‑8 expression. IL‑6 expression was strongly correlated with cell number, whereas IL‑8 expression was moderately correlated with cell number. Additionally, it was observed that co‑cultured cells exhibited a different population of cells, with expression of the mesenchymal stem cell marker cell surface glycoprotein MUC18, indicating a putative role of endometrial mesenchymal stem cells in the secretion of cytokines and disease development. These results indicate a predominant role of primary endometriotic cells in the secretion of cytokines, which contributes to the disrupted peritoneal and endometrial environment observed in the women with endometriosis.