The endotoxin fever (endotoxaemia) in warm-blooded animals is accompanied by complex changes in thermoregulatory, immune, nervous, endocrine systems. It is well known that the endogenous heat shock protein 70 kDa (Hsp70) protects cell and whole organism against different kinds of harmful factors, including endotoxaemia. The goal of this investigation was the study of the effect of exogenous Hsp70 on sleep and thermoregulatory characteristics during the endotoxaemia in pigeons (Columba livia). The endotoxaemia was evoked by the intravenous injection of bacterial endotoxin lipopolysaccharide (LPS) (Escherichia Coli 0111:[Vcy]4 (Sigma); 100 mg/kg). Exogenous Hsp70 (purified from contamination and consisting of constitutive and inducible isoforms) was injected intravenously 15 min before LPS (in dose 80 mg/kg). In the control phosphate buffer was injected intravenously in the same volume as the Hsp70. The recording of polysomnogramm and thermoregulatory characteristics during 24 hours was carried out by computer system. The LPS evoked the increase in the brain temperature, the contractile muscular activity and the total time of non-rapid-eye movement sleep (NREMS) within 5 hours after the injection. The administration of Hsp70 did not change the thermoregulatory characteristics and caused only an increase in NREMS from 2 hour to 4 hour after the start of experiment. The injection of Hsp70 15 min before LPS prevented the rise of the brain temperature and decreased the contractile muscular activity below the baseline but did not change the NREMS amount. Thus we have shown that Hsp70 supressed the febrile response but did not affect the temporal characteristics of sleep and wake states during endotoxaemia. These data suggest that Hsp70 can provide the protective action and probably has a therapeutic potential.