In 4 experiments on retroactive interference (RI), we varied paired-associate learning lists that produced either appreciable or negligible forgetting. When the category of the stimulus word predicted its response word category, and the response was relatively unique within its category, learning was extremely rapid, and negative transfer and RI were negligible. The more the competing primed items in the predicted response category, the slower the learning and the greater the RI. If cues and responses were unrelated, learning was very slow, and RI was appreciable. Thus, predictive relations that help stimuli retrieve unique responses greatly alter forgetting in RI paradigms. This research returns to a fundamental question in the psychology of memory: Why do people forget things they have once learned? One of the oldest, most widely accepted theories of forgetting is associative interference, that people forget some target material because it is interfered with by other material in memory. Traditionally, the principles of associative interference have best been laid bare by studying learning and retention of paired associates, where, in succes- sive lists, subjects learn different responses to the same cues—the so-called A-B, A-C paradigm. The second-learned response, C, is alleged to compete with successful recall of the first-learned response, B. The A-C association supposedly intrudes or wins out in competition with the requested A-B association (for reviews, see Keppel, 1968; Postman, 1961; Postman & Underwood, 1973).