Two studies examined children's first references to the mental states of perception, desire, and belief in themselves and others. In Study 1, children interacted with their mothers in a laboratory setting at 14, 20, and 32 months of age (n=52); in Study 2, children were observed in their homes at 3-month intervals from 18 to 42 months (n=32). Results showed three stages of acquisition, with about a year's delay between each stage. In Stage 1, children acquired the forms for expressing others' perceptions and their own desires. In Stage 2, they began referring to their own perceptions, their own beliefs, and others' desires. In Stage 3, they referred to others' beliefs. There was no general bias toward talking about the self with these mental state verbs, nor any evidence of self-bias in subsequent analyses of children's use of action verbs. Children were not simply mimicking others' use of self and other with mental states. Results pose implications in terms of problems presented for theories regarding how children acquire their first understanding of the mind, theory building versus introspection, and simulation. (Contains 26 references.) (Author/KB)