Instructions given prior to extinction training facilitate the extinction of conditioned skin conductance (SCRs) and fear-potentiated startle responses (FPSs) and serve as laboratory models for cognitive interventions implemented in exposure-based treatments of pathological anxiety. Here, we investigated how instructions given prior to extinction training, with or without the additional removal of the electrode used to deliver the unconditioned stimulus (US), affect the return of fear assessed 24 hours later. We replicated previous instruction effects on extinction and added that the additional removal of the US electrode slightly enhanced facilitating effects on the extinction of conditioned FPSs. In contrast, extinction instructions hardly affected the return of conditioned fear responses. These findings suggest that instruction effects observed during extinction training do not extent to tests of return of fear 24 hours later which serve as laboratory models of relapse and improvement stability of exposure-based treatments.Exposure-based treatments of pathological anxiety, which involve confronting patients with their feared stimulus or situation until the fear response declines 1 , are considered as highly efficient 2 . However, about one third of patients undergoing exposure-based treatments may not experience a clinically relevant decline in their pathological anxiety 3 and another third may experience a relapse, i.e. a return of their pathological anxiety, within 10 years 4 . These findings highlight the relevance of determining factors that moderate both short-term and long-term outcomes of exposure-based treatments. Pavlovian fear conditioning paradigms allow for the investigation of the development, treatment and maintenance of fear under laboratory conditions and typically comprise several experimental phases 5 : During fear acquisition training, a previously unrelated stimulus (conditioned stimulus, CS) is presented together with an aversive event (unconditioned stimulus, US), acquires signal value for the US and eventually elicits a conditioned fear response (CR). During extinction training, the CS is presented without the US and the CR gradually declines which is why extinction procedures serve as a laboratory analogue for exposure-based treatments 6 . Subsequent retention tests which entail the re-exposure to the CS after experimental manipulations and/or a period of time are used to investigate the maintenance of the extinction memory trace. Thus, retention tests are used to model long-term stability of fear reduction and relapse after exposure-based treatments 7 .Verbal instructions about CS-US associations influence conditioned responding when given prior to acquisition training 8 as well as when given prior to extinction training 9 . Instructions given prior to extinction training serve as a laboratory analogue for cognitive interventions which often accompany exposure treatments, e.g., in form of guided threat reappraisal 10 . In general, instructions informing participants about the subsequen...