Many studies suggest that preschoolers rely on individuals' histories of generating accurate lexical information when learning novel lexical information from them. The present study examined whether children used a speaker's accuracy about one kind of linguistic knowledge to make inferences about another kind of linguistic knowledge, focusing specifically on syntax and the lexicon. In Experiment 1, we presented children with 2 live speakers who were lexically accurate, but differed in their appropriate use of subject-verb agreement. Older 4-year-olds, but not younger 4-year-olds, relied on the accurate speaker to learn new labels for novel objects. We suggest only the older 4-year-olds might have registered that the inaccurate speaker was an unreliable source of novel linguistic information. In Experiment 2, 4-year-olds observed 2 speakers whose utterances were syntactically accurate, but differed in lexical accuracy. All 4-year-olds used the speakers' accuracy to guide how they learned novel lexical information and novel irregular plurals, but not how they learned novel irregular past tense forms that children often regularize. These results suggest that when learning novel syntactic information, reliability information might interact with underlying linguistic regularity. (Contains 2 tables.)