This paper reports a study carried out with 14 children (ranging in age from 2.8 to 3.5 years) which investigated children's concepts of difference. Pairs of small objects differing on a number of dimensions were presented to the children. As each pair of objects was presented, children were asked to select the object that was "big,""little,""fat,""thin,""tall,""short." They were also asked to pick one of two index cards with "more" or "less" buttons painted on it and to choose one of a pair of identical objects "before" or "after" a transformation had been performed on it (such as a pair of sneakers, one of which had been tied). The overall performance of the younger and older children was not very different. They were fairly successful with all concepts except "thin,""less," and "before." In follow-up questions with the choice object it came out that the children appear to make more choices in terms of big or little. The data on size adjectives suggest that the children were answering all of the questions with reference to some sort of general or undifferentiated size dimension that they marked as "big" to "little." (MS)