Heart rate (HR), body temperature (TEMP), locomotor activity (LA) and oxygen consumption (O₂C) were studied in awake mice lacking one or both of the adenosine A₁ or A_2A receptors (AR) using telemetry and respirometry, before and after caffeine administration. All parameters were lower during day than night and higher in females than males. Compared to wild-type (WT) littermates, HR was higher in male A₁R knockout (KO) mice but lower in A_2ARKO mice and intermediate in A₁-A_2AR double KO. A single dose of an unselective -blocker (timolol, 1 mg/kg) abolished the HR differences between these genotypes. Deletion of A₁Rs had little effect on TEMP, whereas deletion of A_2ARs increased it in females and decreased it in males. A₁-A_2ARKO mice had lower TEMP than WT mice. LA was unaltered in A₁RKO mice and lower in A_2ARKO and A₁-A_2ARKO mice than in WT mice. Caffeine injection increased LA but only in mice expressing A_2AR. Caffeine ingestion also increased LA in an A_2AR-dependent manner in male mice. Caffeine ingestion significantly increased O₂C in WT mice, but less in the different KO mice. Injection of 30 mg/kg caffeine decreased TEMP, especially in KO mice, and hence in a manner unrelated to A₁R or A_2AR blockade. Selective A_2B antagonism had little or no effect. Thus, A₁ and A_2A adenosine receptors influence HR, TEMP, LA and O2C in mice in a sex-dependent manner, indicating effects of endogenous adenosine. A_2A adenosine receptor plays an important role in the modulation of O₂C and LA by acute and chronic caffeine administration. There is also evidence for effects of higher doses of caffeine being independent of both A₁ and A_2A receptors.