Fifty-two institutionalized mentally handicapped children (average CA of 12 years) were engaged in a study attempting to determine whether there are ordinal dependencies in various scales of developmental milestones or supra-structural behaviors in language, and if so, the degree to which hierarchical levels within given categories serve as functional prerequisites to later levels in the same category. A shadow or blackout method was used in which Ss' language disorders were evaluated in terms of degree of co-absence of various linguistic milestones below their baseline level of development, while other types of paralled behavior were found to be present. The language behaviors considered were those which comprise the first 20 items on the Utah Test of Language Development. Data indicated that the invariable co-absences found should not be attributed completely to chance factory, but should be considered due either to hierarchical dependencies or nosological dependencies. (GW)