This study examined the possibility that lesions of the nucleus accumbens in rats impair the perception of the "cost of reward", as defined by the number of operant responses needed to obtain a food pellet. In a first experiment, visual cues indicated the cost of reward under a multiple-ratio schedule of reinforcement. In a second experiment, the number of lever presses required for each reward incremented with each trial in a progressive-ratio schedule of reinforcement. Lesions of the nucleus accumbens altered the behavioral response to the increasing cost of reward when there was an absence of external cues. There was no change in the ability of the lesioned rats to respond to visual cues that indicated reward availability. The results are considered in terms of the traditional idea of the nucleus accumbens as a limbic-motor interface: it is suggested that, if the nucleus accumbens serves such a function, it is limited to only some contexts.