Previous work on the effect of aging on spontaneous object recognition (SOR) memory tasks in rats has yielded controversial results. Although the results at long-retention intervals are consistent, conflicting results have been reported at shorter delays. We have assessed the potential relevance of the type of object used in the performance of aged rats in SOR tasks. Using standard objects, 24-mo-old rats did not exhibit retention impairment at a 1-h delay. At this retention interval no differences between young and old rats were found in a high-similarity SOR task, but aged rats exhibited deficits when clearly different complex forms were applied.