Self-administered screening questionnaires are available to assist primary care physicians in detecting undiagnosed depression and anxiety disorders. This study used receiver operating characteristic (ROC) analysis to evaluate three such tests: the General Health Questionnaire (GHQ), the Mental Health Inventory (MHI), and the Somatic Symptom Inventory (SSI). Stratified by the results of a preliminary GHQ, 364 health maintenance organization (HMO) members were given these tests and a Diagnostic Interview Schedule (DIS), the latter used as a "truth" standard for current psychiatric diagnosis. The MHI performed significantly better than the GHQ in detecting mental disorders generally and anxiety disorders in particular, and somewhat better in detecting affective disorders. The SSI performed best in detecting anxiety disorders and was significantly better than the GHQ. When subjects who had participated in a previous study involving repeated GHQ administration were excluded, sensitivity of all tests improved, especially the GHQ. We conclude that the MHI can be a useful tool for screening primary care patients, and that the SSI has additional predictive value with respect to anxiety disorders.