Diagnostic reasoning is one of the primary functions of operators in complex technical environments. At present, the options available for assessing the aptitude for diagnostic reasoning are limited to abstract, general measures. However, such methods are perceived as unfair, irrelevant, and may not readily generalize to performance in the domain. The present study outlines a domain-sensitive approach to the assessment of diagnostic reasoning which uses stimuli drawn from the operational environment. Incorporating two tasks, feature identification and feature location, this approach was measured against abstract measures of two individual components of expert reasoning in the context of power system control. The results provide preliminary evidence to indicate that the tasks possess a level of concurrent validity. Implications for theory, research and job assessment are discussed.