3 hr. after training on a 1-way active-avoidance task, 50 adult cats received a combined entorhinal-fornix lesion (hippocampal isolation) or 1 of these 2 lesions alone. A 4th experimental group received the combined lesion 8 days after reaching criterion on the avoidance task. Only the combined lesion, introduced 3 hr. after reaching criterion, led to a significant retention deficit as compared to the control group which was sham operated after the same 3-hr interval. All lesions led to difficulty with the reversal of a position habit, a deficit known to follow the traditional hippocampectomy. Results are discussed in terms of short vs. long-term memory. (22 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)