After eating a meal of poultry a 41-year-old man fell ill with severe diarrhoea, persistent high fever of around 39 degrees C, dehydration and somnolence. On admission to hospital physical examination was normal except for signs of dehydration. The blood count showed a leukocytosis (13,300/microliters) with 60% stab-form neutrophils. The erythrocyte sedimentation rate was raised to 49/82 mm. Also increased were the serum concentrations of creatinine (3.5 mg/dl), creatine kinase (179 U/l), lactate dehydrogenase (298 U/l) and C-reactive protein (16.8 mg/dl). Bacteriological and virological examinations of blood and stool were negative. A normal fluid and electrolyte balance was re-established. But as there was no improvement, ampicillin was administered, 2 g three times daily, then ciprofloxacin, 500 mg two times daily, and finally combined with metronidazole, 500 mg three times daily. Despite this treatment a chest radiograph on the tenth day revealed an infiltration in the left basal lung segment, and the legionella titre became positive at 1:2045. The antibiotic treatment was changed to 150 mg roxithromycin two times daily. The fever fell within 3 days and the diarrhoea stopped after 5 days. He was discharged free of symptoms after 24 days.