The histamine skin test, as modified by Giacovazzo, was carried out on 20 patients with cluster headache and on 20 control subjects, 10 of whom suffered from migraine and 10 who were healthy volunteers not presenting any form of headache. The test was carried out before and after 30 days treatment with timed-release dihydroergotamine methanesulphonate in a dose of 10 mg/day. Data recorded on a "headache time chart" before and after treatment were evaluated by statistical analysis. Block variance analysis was used to evaluate results of three parameters (latency time, hyperemia diameter, extinction time) emerging from the histamine skin test before and after treatment. A statistical comparison was also made of data obtained in basal conditions in the three groups of subjects, in order to confirm the usefulness of this simple test in the diagnosis of cluster headache.