Introduction: Neuropsychological assessment often involves the administration of a number of test instruments yet knowledge of the way in which these tests might interact remains limited. This series of two studies examined the interference effects associated with two very commonly employed measures; the Wechsler Memory Scale –Fourth Edition (WMS-IV) and the Wechsler Adult Intelligence Scale – Fourth Edition (WAIS-IV), with a view to determining proactive and retroactive interference effects associated with these instruments. Method: Ninety-two non-clinical participants in each study were assigned to a two (interference vs. no interference) by two (retroactive vs. proactive) between-subjects design. In Study 1, only the verbal memory components of the WMS-IV using the flexible approach and interference material from the WAIS-IV were employed. In study 2, visuospatial target material was employed. Results: In Study 1, the results indicated a significant retroactive interference effect when verbal material was administered during the delay between immediate and delayed recall. In Study 2, a significant retroactive interference effect in delayed visual recall was noted. When presented proactively, the interference material in each study did not negatively affect memory recall. Conclusion(s): The interference effect of material presented during the delay phase of memory testing significantly impacted upon participants' measured cognitive performance. When using flexible battery approaches, clinicians must be particularly cautious in interpreting results from material presented during any memory delay as this might indicate a spurious diagnosis of a memory disorder. These findings support previous observations that administering conceptually similar material during the delay phase of a memory test will negatively affect memory recall.