Rats on a 23 h food deprivation schedule were trained to run down a straight runway for a food reward. Neither amitriptyline nor mianserine had an effect on the running time for the food reward during the period of continuous reinforcement. However both antidepressants delayed the extinction of this response. It seems unlikely that this effect on extinction was due to an altered motivation for the food reward as amitriptyline significantly decreased the food intake of the experimental animals while mianserine increased the food intake throughout the period of the experiment. The observation that both these antidepressants reduce the speed of extinction of rewarded behaviour may be explicable in terms of observed changes in the concentration of biogenic amines in the limbic system.