This study investigated the ability of high-functioning verbal adolescents with autism or Down's syndrome to perform a referential communication task. It was predicted that autistic subjects would require more specific prompting to convey needed information to a listener than would subjects with Down's syndrome of the same verbal level. Subjects, 13 with autism and 14 with Down's syndrome, matched on verbal mental age, learned a simple board game, and were asked to teach it to a listener who used varying levels of prompting to elicit target information. Most subjects in the autistic group required specific prompting to produce the target information, whereas most subjects with Down's syndrome did not. Response adequacy was significantly higher in the Down's syndrome group than in the autistic group at the most general prompt level. Subjects with Down's syndrome used more gesture at the most general prompt level and when producing high adequacy responses, whereas subjects with autism used more gesture when producing low adequacy responses.