Electroencephalographic methods were used to study the effects of total sleep deprivation on thermoregulatory measures of the fever response in pigeons (Columba livia): brain temperature, peripheral vasomotor reactions, thoracic muscle contractile activity, and the recovery of somatic functions and the time characteristics of waking and sleep in lipopolysaccharide (LPS)-induced endotoxemia. Sleep deprivation during the period in which the quantity of slow-wave sleep increased on administration of LPS induced decreases in the latent period of fever onset and in the duration of fever, along with more significant increases in brain temperature and the level of muscle contractile activity as compared with the effects of LPS alone. The period after sleep deprivation was characterized by more prolonged recovery of muscle contractile activity and the time characteristics of sleep and waking states, along with more prolonged compensatory "rebound" of slow-wave sleep as compared with the effects of sleep deprivation alone. Thus, sleep deprivation in endotoxemia led to decreases in the latent period of fever onset, exacerbation of fever, and increases in the latent period of recovery of physiological functions.