We investigated the effects of diabetes on the spontaneous motor activities (SMA) of streptozotocin-treated rats fed a high-fat diet (HFD), a new nonobese model of type 2 diabetes. The daily changes in the duration of SMA were assessed via infrared cells, which detected all movements of rats that had been fed for 3 weeks with a standard or HFD and then injected with vehicle or 50 mg/kg of streptozotocin. Five to six days after streptozotocin injection, the daily body weight and the levels of duration of SMA of the diabetic rats were depressed, manifest by a substantial decline in the frequency of occurrence of nocturnal SMA episodes. The dramatic depression of daily duration of SMA levels observed in the rats given a HFD and treated with streptozotocin appears to be related solely to the diabetic state and not to body weight and/or HFD consumption, since the HFD (and/or related metabolic effects) remained ineffective in altering this feature in rats that grow normally. By thoroughly separating the prediabetic and the diabetic phases, we have been able to more readily explore the deleterious effects of the stages of both of these phases on changes in daily SMA levels.