In this article the authors present a study of the emitting behavior of carbon nanotube cathodes in a sphere-to-plane field emission diode. A capacitive technique is proposed for the measurement of the anode-cathode distance as well as an innovative analytical procedure for the evaluation of the emitting area. Both anode-cathode distance and emitting area are essential parameters for the analysis of field emission experiments, the interpretation of results, and the extraction of technologically relevant data. Such parameters allow them-to find out the values of turn on fields, current density, and field enhancement factor through the measurement of the emitted current versus applied voltage. Emission tests on single wall carbon nanotube samples with different morphologies have been performed in order to test the procedures and to compare data relative to samples with different morphologies. (c) 2007 American Vacuum Society.