Day-old chickens trained in pairs on an aversive discrimination task yielded a retention function with two points of reduced retention, at 15 and 55 min after learning. These points of temporary reduction in retention were interpreted as reflecting change-over of recall from three successive phases in memory formation. Chicks trained in isolation showed the same retention function as paired chicks except that the second point of reduced retention occurred at 70 min after learning. It was suggested that isolation prolonged the availability for recall of the second phase of memory formation. The findings are consistent with and support a three phase, behaviourally sequentially dependent, model of memory formation previously postulated on the basis of pharmacological studies.