Three studies examined whether 3- and 4-year olds would trust a reliable speaker over an unreliable speaker when learning a new word and whether that trust would be reversed, and the word mapping revised, when a trusted speaker later proved unreliable. Study 1 indicated that 3- and 4-year olds trusted a reliable speaker over an unreliable speaker. Study 2 indicated that some 4-year olds reversed trust and revised a word mapping when a trusted speaker later proved unreliable. Study 3 indicated that those 4-year olds who reversed trust and revised the word mapping were likely to maintain the revision and tended to favor the previously reliable speaker over time. These results are discussed in terms of the role of speaker reliability in young children's word learning. (Contains 3 tables.)