We examined developmental changes in children's inductive inferences about biological concepts as a function of knowledge of properties and concepts. Specifically, 4- to 5-year-olds and 9- to 10-year-olds were taught either familiar or unfamiliar internal, external, or functional properties about known and unknown target animals. Children were asked to infer whether each of four probes, varying in categorical and perceptual similarity to the target, also shared that property. Overall, children made more inferences for known concepts and familiar properties. Older children were more likely to use categorical than perceptual information when making inferences about internal and functional properties of known concepts; however, younger children, in general, made no distinction for property type, and they weighted categorical and perceptual information similarly. Both age groups utilized appearance when making inferences about external properties. Results are discussed in terms of developmental changes in children's appreciation of essentialism. (Contains 1 figure and 4 tables.)