The use of specified diagnostic criteria is part of routine psychiatric practice and research. However, there is evidence that the same criteria may be interpreted and applied differently at different research centers. The next, question is whether it is possible to detect these systematic inter center differences in diagnostic practices. An inexpensive, nonlaborious, standardized method is needed that can easily be used at any site. In the present report, we demonstrate how self-report questionnaires can provide a method of detecting systematic differences in the application of contemporary diagnostic criteria. Sixty consecutively admitted inpatients with nonpsychotic major depressive disorder were interviewed with standardized schedules and diagnosed according to two interpretations of the Research Diagnostic Criteria (RDC) and DSM-III endogenous/melancholia criteria. The patients also completed the Inventory to Diagnose Depression, a self-report scale designed to diagnose major depression and subtype patients according to RDC and DSM-III endogenous/melancholia criteria. The interview to self-report, ratio for diagnosing endogenous depression and melancholia was associated with diagnosticians' interpretation of the criteria. A broader application of the criteria resulted in a higher ratio. A paper-and-pencil questionnaire could be useful in detecting systematic interinvestigator differences in the broadness or narrowness with which criteria are applied. The advantage of a sell-report scale is that it is free from systematic biases and tendencies of clinician raters. Of course, ratings on questionnaires are not free of bias; however, it is less likely that differences between samples will reflect asystematicvariation in response set.