P2X3 protein levels in endometriotic lesions (n = 24, 1.48±0.15) and endometriosis endometrium (n = 21, 1.12±0.11) were both significantly higher than those in control endometrium (n = 16, 0.80±0.09; P<0.05). This evidence concerns the gene P2RX3 and endometriosis.