"Fast mapping" (Carey & Bartlett, 1978) is a hypothesized process enabling children to rapidly create lexical representations for the unfamiliar words they encounter. In this study, 35 normal preschool children, ages 2:1-5:11 (years:months), were exposed to a monosyllabic nonsense word and its novel object referent. On first exposure, 91% of the subjects inferred the connection between the novel word and referent. After this single encounter, 81% correctly identified the referent on hearing its label a second time. After hearing the new word twice, 45% were able to produce at least two of its three phonemes in labeling the novel referent. Of those children who did not attempt to label the novel referent, a significant percentage recognized the correct label. In addition, a significant percentage of subjects recalled some nonlinguistic information associated with the referent. Normal preschoolers appear to create fast mappings containing a great deal of linguistic and nonlinguistic information on the basis of even brief, casual encounters with new words.