Two hundred sixty-five subjects learned a mixed list of paired associates in an AB, AD and AB, CD transfer paradigm. Two levels of semantic processing were factorially varied across original and interpolated pairs. Recall of original pairs was shown to be directly related to the processing depth of original pairs in both paradigms and inversely related to the processing depth of interpolated pairs in the AB, AD paradigm, but not in the AB, CD paradigm. Twenty additional subjects intentionally learned and recalled the same list and showed significant retroactive inhibition for original pairs in the AB, AD paradigm. The findings indicate that interference does not occur in a mechanical fashion, but is sensitive to subjects' level of perceptual analysis of the pairs. (Author)