Hypothesized that, in 5 eyelid-conditioning experiments with a total of 166 male albino New Zealand rabbits, a surprising episode which should itself command rehearsal should also interfere with the rehearsal and learning about other contemporaneous training episodes. In Exp. I and II, it was demonstrated that conditioned responding produced by a series of critical CS-UCS trials was diminished if each trial was followed 10 sec. later by a posttrial episode (PTE) involving a CS-UCS relationship incongruent with S's prior history of training, and thus surprising, but not by a PTE involving the same CS and UCS events in a relationship congruent with S's prior history of training, and thus expected. Exp. III demonstrated that interference with conditioned responding produced by an incongruent PTE was specific to the CS in a list of CS-UCS pairs that the PTE was regularly arranged to follow during training, while Exp. IV and V indicated that such interference decreased systematically as the interval between the critical conditioning trials and their PTEs was lengthened from 3-300 sec. Results are summarized as demonstrating a retrograde interference effect of incongruent as compared to congruent Pavlovian episodes and interpreted as supporting the view that surpising episodes command rehearsal. Additional implications of assuming a variable rehearsal process in animal conditioning, analogous to the process more commonly invoked in treatments of human memory, are discussed. (34 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)