No tolerance to the anorectic activity of d-amphetamine was found in rats given two daily injections of 1.25 mg/kg for 28 days. Such rats also presented no changes in the number of binding sites for serotonin and catecholamines in various brain areas. A 28-day treatment with 10 mg/kg d-amphetamine twice daily caused a significant reduction in the number of binding sites for 3H-dihydroalprenolol (beta adrenergic receptor ligand) in hippocampus, and 3H-spiroperidol (dopamine receptor ligand) in striatum and nucleus accumbens. This treatment did not modify the anorectic effect of 1.25 mg/kg of amphetamine but it markedly reduced the motor hyperactivity induced by this treatment and completely blocked the stereotyped licking and biting induced by apomorphine. Amphetamine stereotypy was not significantly reduced but disappeared faster in chronically treated rats. The possible reasons for the different results (tolerance or sensitization) reported by various authors on changes in amphetamine's effects on motor behaviour during chronic treatment are discussed.