Infants' visual perception of number change was investigated in three studies. These studies focused on infants' perception of events in which the total number of objects in a small group was changed through addition of another object. Involving 60 infants 5 months of age, Study I attempted to determine whether subjects perceived the properties in additions of one object to sets of one or two moving objects as: (1) change versus non-change, (2) the size of the set that was changed, or (3) the number of objects added to a set. A similar study was conducted with 12 infants 15 months of age. Study II, involving 12 infants who were 8 months old and 20 infants 13 months old, investigated whether infants perceived events that involved addition of an object and whether they could discriminate such an addition from a non-change and a larger change. In Study III, 12 infants 13 months of age were involved in an attempt to determine whether they perceived that the addition of one object to a certain set of objects specifies one outcome only. Generally, findings indicated that infants up to 13 months of age seem to be able to perceive components of events that involve number change. Such components were the number that is changed and the size of the change. However, they did not seem to perceive the relationship of such components under a number transformation. (RH)