This study investigated whether continuous light exposure (CLE) results in behavioural disturbances in rats and whether melatonin can modify these potential changes. Four groups of 3-month-old Wistar rats were treated as follows for six weeks: control, melatonin, CLE, and CLE with melatonin. CLE increased systolic blood pressure and melatonin reduced it. No changes in behavioural patterns by CLE were observed. In the controls, melatonin reduced both exploration and locomotion but these parameters remained uninfluenced in the CLE. We conclude that melatonin exerted a different impact on behaviour in controls and in the CLE group.