CD56<sup>+bright</sup> NK cells, constitutively present in human endometrium (eNK cells), represent only 0-2% of NK cells in PBMC, where CD56<sup>+dim</sup> cells dominate.<h4>Method of study</h4>NK-cell subpopulations and NKG2D receptor expression in PBMC were analyzed by flow cytometry in two cohorts of untreated and treated endometriosis patients and healthy age-matched controls.<h4>Results</h4>Elevated numbers of CD56<sup>+bright</sup> cells were observed in 8 of 21 untreated endometriosis patients compared to controls. The gene discussed is NCAM1; the disease is endometriosis.