Maternal language directed to 21 nonhandicapped, 21 Down syndrome, and 19 language impaired preschool children was examined. The three groups (all Caucasian and middle-class) were matched in mean length of utterance (MLU) and in developmental skills as measured on the Vineland Adaptive Behavior Scale. Mother-child language interaction was videotaped for 20 minutes during free play at home. A system of coding the function of language was developed and the videotaped transcripts were coded according to this system. Four distinct types of mother-child directed speech emerged from coding the data: (1) utterances not significantly influenced either by the child's developmental condition or MLU; (2) utterances significantly influenced only by the child's MLU; (3) utterances significantly influenced by the child's developmental condition; and (4) utterances significantly influenced by both developmental condition and MLU. Furthermore, no significant difference in the child-directed speech was found between mothers of nonhandicapped and language impaired children. (Author)