Classical conditioning of rhythmic jaw movements in rabbits is an accepted model of associative learning that may be useful in assessing age-related changes in learning and motivation. A saccharin solution has been thought to be rewarding to rabbits and is often used as an unconditioned stimulus (US). To determine whether age-related differences in preference for saccharin exist, we assessed (a) saccharin versus water preferences and (b) fluid intake level differences (which might account for differing drive levels) in young (4-6 months) and old (31-69 months) rabbits. Young animals demonstrated a significant preference for water, whereas old animals strongly preferred the saccharin solution. There were no differences between young and old rabbits in overall fluid intake. These results suggest that whereas saccharin may be an appetitive US for old rabbits, it may be aversive to young ones. Thus aging may affect the incentive value of rewarding stimuli, complicating the interpretation of interactions among aging, learning, and motivational processes.