Sleep deprivation causes an increase in energy expenditure in animals. Thyroid gland function has been related to metabolic function, and this may be compromised in sleep manipulations. The objectives of the present study were the following: 1) to develop a model of hypothyroid rats by surgical removal of thyroid glands without extirpation of the parathyroid; 2) to observe the sleep architecture in euthyroid (Etx) and hypothyroid (Htx) rats, both before and after rapid eye movement (REM) sleep deprivation (96 hours); 3) to challenge both groups (i.e. Etx and Htx) with REM sleep deprivation (96 hours) and then evaluate the effects on temperature; and 4) to measure the levels of adenosine and thyroid hormones in blood. One-month-old Wistar male rats (weight 90-100 g) were studied. The thyroid gland was removed, and the parathyroid glands were reimplanted within the neck muscle (Htx) under halothane anesthesia. A sham-operated group was also included (Etx). Four months later, the animals were studied according to the following protocols. Protocol 1: Animals of both groups (i.e. Etx and Htx) were implanted for sleep recordings. After a baseline polysomnography, these animals were REM sleep deprived by the platform method (96 hours). Protocol 2. An intraperitoneal temperature transducer was placed into animals of both groups under deep halothane anesthesia. They were studied at baseline, during 96 hours of REM sleep deprivation, and on the rebound period. Protocol 3: Plasma thyroid hormones [T3, T4, and thyroid-stimulating hormone (TSH)] and plasma adenosine were determined in both groups. Results of protocol 1 indicated that the main difference observed in Htx rats during the baseline sleep was an increase in delta sleep (slow-wave sleep 2) and a reduction in waking time compared with Etx animals. REM sleep rebound after 96 hours of REM sleep deprivation was similar in both groups. In protocol 2, the main finding was that Htx animals had reduced body temperature. A significant difference in body temperature between Etx and Htx animals was found mainly during lights-on period. REM sleep deprivation in the Etx group produced an increase in body temperature. Htx animals showed the opposite effect, with a reduction in body temperature during and after REM sleep deprivation. In protocol 3, the main findings were that Htx animals exhibited a significant reduction in blood thyroid hormones (T3, T4), and that they also had high levels of plasma adenosine. REM sleep deprivation produces changes in temperature regulation. The increase in body temperature during REM sleep deprivation may require thyroid integrity. Absence of the thyroid gland does not seem to influence REM sleep recovery after its deprivation. The high plasma adenosine levels found in the Htx group may explain the increase in delta sleep in this group.