The Inventory for Depressive Symptomatology (IDS) is a new measure of depressive signs and symptoms. Both self-report and clinician-rated versions are under development. The IDS-SR (self-report) was completed by 289 patients, 285 of whom were outpatients. Unipolar major depression (n = 174), bipolar disorder (n = 44), euthymic (S/P unipolar or bipolar) depression (n = 33), and other psychiatric disorders (n = 38) were included. The IDS-SR had good internal reliability (coefficient alpha = 0.85), and significantly correlated with both the Hamilton Rating Scale for Depression (HRSD) (r = 0.67) and the Beck Depression Inventory (BDI) (r = 0.78). The clinician-rated IDS (IDS-C) was administered to 82 outpatients (75 with unipolar or bipolar disorder, 5 with other psychiatric disorders, and 2 euthymic (S/P unipolar) depressions). Coefficient alpha (0.88) suggested strong internal consistency. The IDS-C correlated highly with both the HRSD (r = 0.92) and the BDI (r = 0.61). Discriminant and factor analyses provided evidence for construct validity for both the IDS-C and IDS-SR. Both scales significantly differentiated endogenous from nonendogenous depression defined by Research Diagnostic Criteria (RDC). Factor structures for the IDS-SR revealed four factors: mood/cognition, anxiety, selected endogenous symptoms, and hyperphagia-hypersomnia. The IDS appears applicable to both inpatients and outpatients with endogenous, atypical, and nonendogenous major depression, and may have utility with dysthymics.