TOMASELLO, MICHAEL, and MANNLE, SARA. Pragmatics of Sibling Speech to One-Year-Olds. CHILD DEVELOPMENT, 1985, 56, 911-917. Very little research to date has been concerned with characterizing the nature or the effect of the linguistic interactions between beginning language learners and their older siblings. Although it has been suggested that 3-5-year-old preschoolers do adjust structural characteristics of their speech for infants, there are indications that they may not make adjustments in the pragmatic domain. The current study, therefore, was designed to explore sibling-infant linguistic interaction with a special emphasis on pragmatic factors. 10 infants were videotaped twice, once at 12-18 months and once at 18-24 months, in free play with their mothers and with their preschool-age siblings. Compared to mothers, siblings were highly directive in their linguistic interactions and showed little inclination to provide the infant with nonverbal information. They did not adjust the length and complexity of their utterances over time, as did the mothers. Conversations between siblings and infants were short or nonexistent and contained few of the conversationmaintaining devices that mothers used. The directiveness of siblings and their nonresponsiveness in conversations may contribute to the tendency of some later-borns to employ expressive styles of language acquisition.