A double-blind, cross-over, placebo-controlled study of betahistine dihydrochloride (12 mg, t.i.d.) was carried out in patients with vertigo of peripheral vestibular origin. Twenty-four patients completed the study, which consisted of two six-week treatment periods. The patients were diagnosed as suffering from Menière's disease (15 patients), vertigo due to other (specified) causes (five patients), or vertigo of unknown origin (four patients). Patients were examined by the investigator at the start of the study and were re-assessed at three-weekly intervals. In addition, they recorded the nature, frequency and severity of their symptoms on diary cards. Both the incidence and severity of dizziness (the predominant presenting complaint) were found to be significantly reduced during betahistine treatment (p = 0.004). The occurrence of nausea and vomiting was also significantly reduced during betahistine treatment (p = 0.014 and 0.036 respectively). There were no statistically significant differences in the results of audiometric or vestibulometric tests, or in the severity of tinnitus or deafness, between the two treatment periods. The overall comparisons of the two periods made by both the patients and the investigator were significantly in favour of betahistine (p less than 0.001). All diagnostic groups responded favourably to betahistine, confirming the efficacy of betahistine in the symptomatic treatment of peripheral vestibular vertigo. No unwanted signs or symptoms were reported.