The specific symptoms that have been felt to characterize schizophrenia have varied widely over time and across cultures, as has the diagnostic and prognostic importance placed on these symptoms. In this report, the historical concepts of what constitutes the "characteristic symptoms" of schizophrenia are reviewed in the context of the development of DSM-IV. Through the existing literatures as well as through previously unpublished data sets, the dimensions of reliability, specificity, validity, and descriptive value of the various signs and symptoms used to classify schizophrenia are explored. In addition, the structure of the DSM-III-R definition of schizophrenia with that of the proposed revisions of the International Classification of Diseases (ICD-10) are contrasted, demonstrating several potentially meaningful differences. It is concluded that a comprehensive description of the signs and symptoms of schizophrenia should place a strong emphasis on both positive and negative symptoms. Principles and approaches to guide the development of DSM-IV are suggested.