A retrospective study of the histories of 100 patients with biopsy-proven giant cell arteritis was performed. Fifteen of these patients had "fever of unknown origin" as the initial manifestation of this disease. All 15 had normal leukocyte counts; however, they had significantly lower hemoglobulin and albumin levels (P greater than 0.01) and significantly higher platelet counts, erythrocyte sedimentation rates, and alkaline phosphatase values (P congruent to 0.05) compared to the other 85 patients. In 4 patients, random temporal artery biopsies were performed despite persistently negative results from diagnostic evaluations and in the absence of any symptoms or findings suggestive of arteritis.