The effect of central angiotensin AT₁ receptor blockade on thermoregulation in rats during exercise on a treadmill (18 m.min^-1, 5% inclination) was investigated. Core (T_b) and skin tail (T_tail) temperatures were measured in rats while they were exercising until fatigue after injection of 2 µL of losartan (LOS, 20 nmol, n=4; 30 nmol, n=4; 60 nmol, n=7), an angiotensin II AT₁ receptor antagonist, or 2 µL of 0.15 mol/l NaCl (SAL, n=15) into the right lateral cerebral ventricle. Body heat rate (BHR), heat storage rate (HSR), threshold T_b for tail vasodilation (TT_bV), time to fatigue (TTF) and workload (W) were calculated. During exercise, the BHR and HSR of LOS-treated animals were, respectively, 40% and 53% higher (p<0.01) than in SAL-treated animals. Additionally, rats injected with LOS showed an increased TT_bV (38.59±0.19° C, LOS vs 38.12±0.1° C, SAL, p<0.02), a higher T_b at fatigue point (39.07±0.14° C, LOS vs 38.66±0.07° C, SAL, p<0.01) and a reduced running performance (27.29±4.48 min, LOS vs 52.47±6.67 min, SAL, p<0.01), which was closely related to the increased BHR. Our data suggest that AT₁ receptor blockade attenuates heat dissipation during exercise due to the higher TT_bV, leading to a faster exercise-induced increase in T_b, thus decreasing running performance.