The major methodological innovation of DSM-IV is its emphasis on three stages of empirical documentation 1) literature reviews; 2) reanalyses using available data collected at multiple sites and 3) field trials. This proposal describes 15 DSM-IV test each focused on a diagnostic question of great importance identified in the first stage Field tests will generally each occur at five sites with approximately 500 patients. Diagnoses were selected for field testing when there are major inconsistencies between their DSM-III-R and ICD definitions and/or when major changes are anticipated for DSM-I In most instances, the field test will compare the reliability, feasibility, descriptive validity, and the performance characteristics of the DSM-III, DSM-III-R and ICD definitions with a criteria set derived empirically from the literature and/or data reanalyze Validity data (onset, course, family aggregation, demographic differences, biological Test results, and treatment response) will be collected when possible. The field trial will also provide data on the overlaps amongst systems and their impact on prevalence a crosswalking. DSM-IV field trials represent an advance over previous field trials because they will 1) culminate a three stage process of empirical documentation and will answer more focused questions;2)compare alternative possible systems (DSM and ICD) with empirically derived definitions;3)have more careful quality control and 4)will be conducted by the leading experts for each diagnosis. Because field trials are a bridge between findings generated in clinical research and decisions meant for clinical practice, they differ from traditional clinical research in that 1) reliability is an outcome variable, not a precondition to beginning the test; 2)patients are selected in a way that is representative of clinical practice to ensure that difficult to define, boundary patients are not excluded; and 3)tests are conducted at multiple sites on large numbers of patients and with diverse comparison groups. The current proposal attempts to increase the rigor and scope of field trials and to use the data collected through field ,trials as additional empirical evidence in making choices and in reconciling available alternative diagnostic definitions.