Psychophysiological measures have the potential to supplement and eventually replace subjective measures in determining fatigue and workload in military and commercial systems during test and evaluation. With the advances in equipment (such as miniaturization) over the last decade, the use of various psychophysiological methods, particularly electroencephalography (EEG), has become more feasible in operational settings. Accompanying this capability is the necessity to develop valid methodology and ensure consistent results within individuals and similar situations using relatively automatic analysis and presenting the results in non-specialist terms. This paper reviews the rationale for using psychophysiological metrics, particularly EEG, during the test and evaluation process, and discusses the requirements for its use and acceptance by decision-makers and subjects. The comments in this paper are based on 14 years of observation.