Rats with lesions in the ventromedial nucleus of the hypothalamus displayed significantly greater positive behavioral contrast effects than did controls on a multiple VI extinction schedule, supporting the hypothesis that animals with ventromedial lesions are more responsive than controls to changes in reinforcement contingencies. Also supporting this hypothesis was the finding that three of the four lesioned animals displayed negative behavioral contrast effects on a multiple VI VI schedule which followed the multiple VI extinction schedule, whereas none of the five control animals displayed negative contrast. Manipulations involving shifts in reinforcer quality were inconclusive. It was concluded that some of the current hypotheses regarding the behavioral consequences of ventromedial lesions are in need of revision. Several studies have demonstrated that animals with ventromedial hypothalamic (VMH) lesions show greater reactivity to the positively reinforcing and aversive properties of stimuli than do control animals. For example, the occurrence of overeating normally seen in VMH-lesioned rats critically depends upon the taste qualities of the diet which the animals are fed (Corbit & Stellar, 1964; Graff & Stellar, 1962; Teitelbaum, 1955). While normal animals will consume appreciable amounts of cellulose- or quinine-adulterated food, obese hyperphagic rats will stop eating and lose a great deal of weight (Graff & Stellar, 1962). Obese hyperphagic animals will also show a marked increase in food intake over their own control levels if their food is sweetened with dextrose (Teitelbaum, 1957). Other studies have corroborated these findings for animals in either the dynamic or static phases of hyperphagia, showing that they react exaggeratedly to the taste qualities of both food (Corbit & Stellar, 1964) and water (Corbit, 1965). Furthermore, intragastric feeding studies have demonstrated that although unoperated rats can regulate food and water intake in the absence of taste and smell, VMH-lesioned animals are critically affected by the absence of taste (Epstein & Teitelbaum, 1962; Teitelbaum & Epstein, 1963). The exaggerated finickiness shown by animals with the VMH area destroyed has been used to support the thesis that VMH lesions produce a basic motivational disturbance evidenced by increased sensitivity to the reinforcing properties of sensory stimulation. According to Grossman (1966, 1967), the effects of VMH lesions on feeding behavior may be secondary to a more general change in the organism's affective responsiveness to all stimuli.