Design factors are considered for the use of emitting and nonemitting metallic probes for measuring static potential in electron streams. Both unneutralized streams and those neutralized by positive ions in a field free drift space are considered. Experimental results are given for potential measurements in a cylindrical diode and in a beam type tube. Good agreement with theory is found for the radial potential distribution in the diode using either probe. The emitting probe gives best results but is more complex in construction and circuitry. Qualitative agreement with theory is found for axial and radial potential distribution in a neutralized cylindrical electron beam.