Positive‐ion effects have been observed in pulsed electron beams of short duration (0.5 to 5 microseconds), under conditions of operation normally encountered in high‐power microwave tubes. Three different aspects of ion effects were studied; (1) beam focusing, (2) ion oscillations, and (3) ion trapping at scallop minima. Experimental results are given and correlated with previous work on ion effects by other authors.