A new technique is described for measuring the charge distribution of an electron beam in a magnetic field. The method is especially applicable to the long, thin, high‐current beams commonly used in traveling wave tubes and backward wave oscillators. It consists of making the beam trace out its own characteristics by sweeping it across a pinhole in crossed electric and magnetic fields. The data are presented in the form of oscilloscope pictures of the actual charge distribution. Quantitative measurements of the charge distribution are also obtainable.