Research is being conducted to determine the factors behind linguistic retardation in children. A first question raised was whether the linguistic system of the deviant child is qualitatively different from that of a normal child. A matching-up of deviant and normal children according to linguistic level suggests that the onset of base syntax may be delayed in the deviant child by three and a half years, and that the time needed to pass from one level to another may be two and a half years longer in the deviant child. A further study showed that the deviant and the normal group had similar organization of phrase structure grammars, but that the deviant group did not use major linguistic categories in as many different contexts as the normal group. To determine what this information could relate about the nature of the deviant child's deficit, utterances are being collected and analyzed on the basis of semantic categories. Preliminary analysis suggests the deficit lies in the ability to develop additional terms and relationships in which to use them. This information leads to the question of a cognitive deficit. Experimentation tends to support the idea that linguistic level and symbolization correspond more closely in deviant children than linguistic level and general nonverbal development. A final hypothesis is that children with linguistic deficits reflect a base representational rather than a base intellectual deficiency, and that diagnostic tests should reflect this pattern. (AM)