AbstractTwo chimpanzees (Pan tryglodytes), Fanny and Jane, were presented with liquid and number conservation problems. One chimpanzee, Jane, was successful in solving both sets of problems in that she was not distracted by irrelevant transformations, being influenced only by changes in quantity. Her success appeared to be based on the ability to make inferences rather than on simple perceptual judgement of the final comparison. The results are compared and contrasted with those of Premack, in G. Woodruff, D. Premack, and K. Kennel [(1978). Conservation of liquid and solid quantity by the chimpanzee. Science, 202:99–994] and J. Mehler and T. G. Bever [(1967). Cognitive capacity of very young children. Science, 158:141–142; (1968). Quantification, conservation and nativism. Science, 162:979–981], and it is suggested that there may be a similarity of conservation development between chimpanzees and man.