AS PER AMENDMENT 10/24/96: To develop a domain/construct-driven neuropsychological and neurological battery. Scaling of instruments to allow measurement of functions from infancy to early adulthood; establish reliability and validity of the new instruments developed for the NIMH Neurodevelopmental Battery. Downward extension of cognitive domains into infancy and early childhood. To describe and compare outcomes when assessing level of development versus rate of change. Describe and compare the outcomes from a global assessment of neurodevelopment (e.g., a standardized I.Q. score) versus discrete assessments (e.g., functional domains such as motor or language skills). Develop guidelines for multicultural neuropsychological and neurological assessment within a clinical trials design. Describe the nature of impaired developmental abilities and course of the disease in infants and children.