In this study, mental terms in mothers' and their children's speech at two and three years of age were studied in order to examine the relationships between maternal and child use. Nineteen mother and child dyads were videotaped for one hour on each of two days when the children were 2;0 and again for two one-hour sessions on separate days when they were 3;0, and mental terms were noted. The utterances in which mental terms were used were coded for function. Results supported the existing picture of children's mental term use. Few terms appeared at 2;0, but many were used at 3;0 with think and know predominating. Mental terms occurred more commonly in utterances used to regulate the interaction between the participants than in utterances referring to mental states. Children's mental term use mirrored that of their mothers. Further, mothers' use of mental terms for particular functions when their children were 2;0 predicted their children's use at 3;0. While allowing no conclusions about causation, our findings suggest that the development of mental state language, and thus presumably a theory of mind, is fostered by the linguistic environment. Specifically, it is argued that the tendency of mothers to focus their children's attention on mental processes by talking about them and, more importantly, by using utterance types which conceivably direct the children to reflect on their own mental states, is associated with children's use of mental terms.