A 36-year-old man, with a history of recurrent respiratory infection, dermatomycosis, arthralgia and abnormal stools for 12 years, developed a febrile illness (up to 40 degrees C). A Serratia marcescens septicaemia responded to antibiotics. Four months later cervical and abdominal lymph-adenopathies were noticed. Cervical lymph node biopsy revealed lymphadenitis with epithelioid cell nests. Duodenoscopy with biopsy demonstrated Whipple's disease associated with lambliasis. Electron-microscopy showed rod-shaped bacteria typical of Whipple's disease, and Giardia lamblia. Using the polymerase chain reaction, Whipple-specific DNA fragments of 284 base pairs from the genome of the Whipple bacterium (Tropheryma whippelii) were demonstrated. Antibiotic treatment with Ampicillin (2 g three times daily) and ceftriaxone (2 g once daily) i.v. for 21 days, followed by oral ofloxacin (200 mg daily) and co-trimoxazole (three times daily 800 mg sulfamethoxazole and 160 mg trimethoprim), brought about remission of Whipple's disease. Long-term antibiotic treatment was continued with co-trimoxazole. Lambliasis recurred after 3 and 5 months, despite treatment with metronidazole, 250 mg three times daily for 7 days.