The positive-negative distinction has emerged as a meaningful basis for understanding the heterogeneity of schizophrenia and treatment alternatives, but its delineation requires carefully devised, well validated techniques. This article considers the psychometric requisites for such an instrument and describes 30 criteria associated with operationalization, scale construction, and standardization. Six prominent positive-negative scales are compared on these criteria, and most are found deficient in terms of: a formalized interview procedure; detailed definitions for levels of symptom severity; exclusion of "secondary" negative symptoms; comparative scales to assess positive symptoms, depression, and global severity of illness; broad sampling of negative symptoms; large scale standardization studies; and determination of multiple facets of reliability and validity. The Positive and Negative Syndrome Scale (PANSS) is described as an effort to approach these principles of test standardization, and its clinical and research applications are discussed.