Abnormalities in infant sleep and wake state characteristics have been linked to aberrant central nervous system function. We present an overview of the development of normative sleep-wake state characteristics in fullterm infants, and atypical state characteristics as presented in several clinical populations including: preterm infants, infants at risk for sudden infant death syndrome, autistic children, and people with other developmental disabilities. We review and critique the research literature on the usefulness of infant state parameters in the prediction of developmental outcome of infants with biological risk, and offer suggestions regarding future research in this area. (C) 1995 Academic Press, Inc.