This study was designed to investigate the effects of environmental stress on metabolic derangements and the expression of diabetes phenotype in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an animal model of human type 2 diabetes (NIDDM). Acute environmental stress, i.e., exposure to water with immobilization for 1 h, caused a transient increase in blood glucose with decreased insulin secretion, and the stress-induced hyperglycemia augmented with age. The increased glycemia was associated with increased plasma levels of catecholamines and corticosterone. Short-term stress, the same stress of 1 h/day for 10 days, caused a significant decrease of food intake, which led to weight reduction in OLETF rats, aged 50 weeks. Blood glucose and insulin responses in OGTT showed no change before or after the short-term stress, despite the weight reduction. In chronic stress experiments, i.e., exposure to the same kind of stress for 6 days/week from 8 to 75 weeks of age, stressed rats did not gain weight, compared to control rats. Blood HbA1c levels and the index of insulin resistance after a 4-h unfed period were significantly lower in stressed rats than in controls from 35 and 45 weeks of age on, respectively. The occurrence of diabetes, diagnosed by OGTT, was also significantly lower in the rats subjected to chronic stress than in controls. These results suggest that chronic stress from 8 weeks of age inhibited weight gain, probably due to changes in eating behavior, preventing the deterioration of insulin resistance in OLETF rats. Plasma leptin levels were not modulated by stress, and correlated with body weight in the rats under chronic stress and in controls. These results suggest that in type 2 diabetes, blood glucose derangement due to stress is presumably associated not only with changes in counterregulatory hormones involved in glucose metabolism, but also with stress-induced changes in eating behavior.