Duplex sonography of the temporal artery may be helpful in the diagnosis of cranial arteritis. The superficial temporal arteries of 36 patients with cranial arteritis or suspected arteritis were examined using both duplex ultrasonography (US) and biopsy. The data of these patients were divided into two groups. Group A consisted of 24 patients (66.7%) with definite positive results using duplex (US) and Group B of 12 patients (33.3%) who showed a suspicious or negative ultrasonographic result. In all patients of Group A, the histological findings corresponded with the ultrasonographic changes in the inflamed artery. - The characteristic ultrasonographic sign was a dark halo around the lumen of the temporal arteries. There was a high correlation between a bilateral halo found by US with an ocular involvement. Ten out of 14 patients with a bilateral halo (71.4%) showed a distinct involvement of the optic nerve or retina. - The characteristic histological signs were infiltration of the vessel wall by inflammatory cells, mainly lymphocytes. Group B: The biopsies of the superficial temporal arteries were positive in 8 patients (66.7 %), negative in 4 other patients (33.3%). Patients with a distinct halo, demonstrated by US, also showed corresponding pronounced inflammatory cell infiltration of the vessel wall. Patients with no ultrasonographic changes presented histological signs of initial inflammation such as isolated inflammatory cells around the vasa vasorum and/or in the adventitial layer.