When samples with undetectable peritoneal fluid levels of MICA, MICB and ULBP-2 were excluded, MICA and MICB levels were significantly higher in endometriosis patients than in controls (median, 1.1 pg/mg; range, 0.1–143.5 vs. median, 0.6 pg/mg; range, 0.1–3.5; P = 0.003 for MICA; median, 4.6 pg/mg; range, 1.2–4702 vs. median, 3.4 pg/mg; range, 0.7–20.1; P = 0.001 for MICB). Here, MICB is linked to endometriosis.