A typical case of Whipple's disease was manifested by malabsorption and nondeforming peripheral arthritis for five years. A definite diagnosis was made by duodenal mucosal biopsy which revealed the characteristic histologic features by light microscopy, intracellular and extracellular Whipple's bacilli by electron microscopy, and a typical immune cross-reactivity pattern by immunofluorescence technique. Whipple's bacilli apparently elicit no effective humoral and cellular immune response; macrophages thus play the key role in its pathogenesis. Antibiotic treatment resulted in a dramatic relief of symptoms and rapid restoration of body weight. We stress that in patients with nondeforming peripheral arthritis associated with malabsorption syndrome, Whipple's disease, despite its rarity, should be included in the differential diagnosis.