Microdialysis was performed to quantitate lateral hypothalamic dopamine (LHA DA) release before, during and after a single meal in food-deprived obese and lean Zucker rats to examine our hypothesis that an abnormally high dopamine activity may exist in the LHA of obese Zucker rats. Food consumption after food deprivation, was significantly greater in obese than in lean rats (4.1 +/- 0.2 and 2.3 +/- 0.4 g, respectively; (p < 0.05). Mean basal dopamine level was significantly higher in obese than in lean rats (12.0 +/- 0.3 and 10.5 +/- 0.3 pg in 10 microliters dialysates, respectively; p < 0.05). Dopamine release during eating was greater in obese than in lean rats (159.1 +/- 6.8% and 135.4 +/- 3.6% of baseline level, respectively; p < 0.05). After eating, the dopamine level returned to that before (105.6 +/- 4.5% in obese rats and 101.9 +/- 4.0% in lean rats) within the first 20 min sample. Data suggest that there may exist an inherently higher LHA DA 'threshold' level in obese Zucker rats and that until it is reached, food intake continues. This higher 'threshold' level may be responsible for their unique feeding behavior and is probably a contributory factor to their development of obesity.