Endogenous opioids are known to be involved in the pathophysiology of idiopathic headache. In fact, decreased levels of enkephalin (E) or endorphin (BE) during headache attacks might be a marker of an altered pain-inhibiting system of central neurotransmission or could be secondary to alterations of brain circulation that often occur during the headache crisis. Recently, captopril (C) has been shown to be apt to restore the availability of endogenous opioids, to improve cerebral blood flow via the inhibition of both the cerebral and systemic renin-angiotensin system or of catecholamine release. It has also been reported to be able to restore the nociceptive-antinociceptive balance through an increase of serum kinin (K) or prostaglandin (Pr) levels. In the present study, the efficacy of C in reducing the frequency (F), duration (D), or severity (S) of headache paroxysm were investigated in a double blind trial vs. placebo (P). Twenty-six subjects (5 males and 21 females; mean age 37 +/- 11 years) suffering from idiopathic headache at least for one year have been allocated to treatment with C (25 mg three times/day) or P according to a double-blind randomized protocol for 4 months. The effects of C or P have been evaluated with Migraine Index Correct, related to changes in F, D or S of headache attacks. Our results indicate that C is effective in reducing F, D or S in subjects with idiopathic headache.