The aim of the experiments was to determine whether chronic pretreatment with viloxazine decreased the sensitivity of mice to the sedative effects of a beta agonist clenbuterol. Mice were subjected to chronic oral treatment with viloxazine (128 mg/kg twice daily) and then given a single administration of 32 mg/kg PO followed by clenbuterol (0.125 mg/kg IP) before being tested in a standard photocell activity meter. Imipramine, administered at the same doses in the same experimental conditions, was used as a comparison compound. The results showed that chronic but not acute viloxazine decreased the hypoactivity induced by clenbuterol, suggesting the induction of beta receptor subsensitivity. With imipramine the results were in the same direction but less clear. The findings are discussed in terms of the eventual specificity of the viloxazine effect to subsensitivity in beta-2 receptors.