We examined scratch-inducing effects of intracisternal, intrathecal and intradermal injections of morphine and some opioid agonists in mice. Intracisternal injection of morphine (3 nmol/animal) and the -receptor agonist [D-Ala², N-Me-Phe⁴, Gly⁵-ol]enkephalin (DAMGO; 0.2 nmol/animal) elicited scratching of the face, with little effect on scratching of the trunk. Intracisternal injection of the -receptor agonist [D-Pen^2,5]enkephalin (DPDPE) and the -receptor agonist U50488 were without effects. Intrathecal injection of morphine (0.1–3 nmol/animal) produced a dose-dependent increase in body scratching, with little effects on face scratching. Face scratching induced by intrathecal morphine (3 nmol/animal) was almost abolished by subcutaneous pretreatment with naloxone (1 mg/kg). Intradermal injections of morphine (3–100 nmol/site), DAMGO (1–100 nmol/site), DPDPE (10 and 100 nmol/site) and U50488 (10–100 nmol/site) did not elicit scratching of the site of injection. Intradermal injection of histamine (100 nmol/site) induced the scratching in ICR, but not ddY, mice and serotonin (30 and 50 nmol/site) elicited the scratching in either strain of mice. The results suggest that opioids induce scratching, and probably itching, through central -opioid receptors in the mouse.