Research and practice on augmentative communication for persons with moderate or severe mental retardation have primarily targeted the acquisition and use of single symbols. Symbol combinations, however, provide insight into how augmented communicators use individual symbols to build more complex communications. In Study 1, untaught symbol combinations produced during natural communication interactions by 7 subjects with mental retardation were examined for their semantic, ordering, and generalization patterns. The symbol combinations largely resembled those produced by young speaking language learners, suggesting that the augmented communicators were following typical patterns of communication in generating their symbol combinations. In Study 2, we examined the symbol combinations modeled for subjects by their partners. The structure of the modeled combinations did not resemble the children's productions, indicating that the children could not have relied on simple rote imitation for their combination production. These results suggest that augmented communicators with mental retardation may use their symbols as speaking children use oral words in the development of complex communications.