Behavioural assessment of mice lacking adenosine A₁ receptors (A₁Rs) showed reduced activity in some phases of the light–dark cycle, reduced exploratory behaviour in the open‐field and in the hole‐board, increased anxiety in the plus maze and dark‐light box and increased aggressiveness in the resident‐intruder test. No differences were found in spatial reference and working memory in several Morris water maze tasks. Both mutant mice had reduced muscle strength and survival rate. These results confirm the involvement of adenosine in motor activity, exploratory behaviour, anxiety and aggressiveness. A₁Rs also appear to play a critical role in ageing‐related deterioration.