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The reason why the Herbig Ae-Be stars emit X-rays is not understood. A popular scenario is that the Herbig Ae-Be stars are not the sources of this emission comma but rather the X-rays come from unresolved low-mass companion stars openParT-Tauri starsclosePar. However comma our archival study shows that the most luminous Herbig Ae-Be stars can emit X-rays much above what is seen from T- Tauri stars comma suggesting that -- at least for the most luminous L>10elev3 comma L_keyOpen odotkeyClose Herbig Ae-Be stars -- some other mechanism must be responsible for the X-ray emission. Only 8 Herbig Ae-Be stars in this key luminosity range have been observed in X-rays comma and thus we propose a survey for XMM-Newton to measure the X-ray luminosities of a sample of 24 additional luminous Herbig Ae-Be stars.