The performance of seven Mullard channel electron multipliers, or `worms', and one Bendix magnetic electron multiplier was studied for a period of several thousand hours at a pressure of 2 ntorr. Reductions in the mean overall gain of the magnetic electron multiplier by a factor of four, and for the worms by factors of ten to one hundred are observed. Storage under vacuum and at atmospheric pressure show the fatigue effect to have both a reversible and a nonreversible component. The effect of loss of gain on the response of the multipliers when used as satellite xuv photon detectors is discussed.