The overconsumption of rich and palatable foods and "yo-yo" dieting are feeding patterns involved in obesity and possibly hypertension in humans. We therefore examined the effects of diet-induced obesity and weight cycling on the blood pressure and heart rate levels of 60-day-old male normotensive Sprague-Dawley (S-D) and spontaneously hypertensive (SHR) rats. Six months on a high-fat and high-sucrose diet (HF/M) produced a greater obesity in S-D rats than in SHR rats. The caloric intakes of S-D rats fed the HF/M diet were greater than the caloric intakes of pellet-fed controls, whereas those of SHR rats were similar. The obesity of both strains was associated with hyperinsulinemia, heavier white (retroperitoneal) and brown (interscapular) fat pads, heavier heart weights, and tachycardia. Despite these changes, diet-induced obesity failed to increase systolic blood pressure obtained under light ether anesthesia or mean arterial pressure in the conscious state. Paradoxically, the blood pressures of SHR rats fed HF/M diet were reduced perhaps as a result of the high polyunsaturated fat component of the diet. A second S-D dietary obese group was alternated between 2-wk periods of unrestricted HF/M diet and 50% restricted pellet chow. Although their body weights were similar to pellet-fed controls, three cycles of weight loss and weight regain resulted in the consumption of increased dietary fat, increased food efficiency, heavier fat pads, and hyperinsulinemia. Heart rate and to some extent blood pressure fluctuated with diet, being elevated during HF/M feeding and reduced during restricted pellet feeding. Although weight cycling intensified the physiological responses to food ingestion, we found that weight cycling in dietary obese S-D rats did not elevate blood pressure levels.