The results of the developmental assessment of nine Down's infants are very similar to previous evaluations of Down's infants. Since developmental age and chronological age are very negatively correlated, the supposition is that at some point in time the Down's infant is not so retarded. Current and past evaluations support this view. The onset of developmental delay in Down's seems to occur at 4-6 months of age, the age when most infants show a shift from subcortical to cortical control of behavior.