A revised interference theory interpretation of unlearning is presented which is based on an explicit storage-retrieval model. The theory holds that the first and second lists are stored as separate memory units. Intrusions of first-list items during second-list learning are viewed as allowing the opportunity for dual storage of the first-list item within both memory units. In standard retroactive inhibition experiments in which no special cues for list discrimination are provided, the major factor which produces unlearning is held to be the S's inability to retrieve the first-list memory unit.