In a curtate‐cycloidal‐focusing mass spectrometer, the first‐order effect of space charge is not to impair the quality of the focus but to shift the focal point out of the plane of the resolving slit. For a given ion mass and ion current, the magnitude of the effect is about four times as large in a cycloidal‐focusing instrument as in a 180° magnetic sector mass spectrometer operating in the same magnet.