In 1987 and 1988, 340 consecutive patients attended the endoscopy centre of Cochin hospital, Paris, and underwent oesophago-gastroduodenal endoscopy in a search for Giardia lamblia parasitology and histology. Two-hundred and eight of these patients presented with non-ulcer dyspepsia and entered a prospective study aimed at determining the advisability of a systematic search for Giardia lamblia in this population. Six biopsies were positive for giardiasis, including 3 in patients with acquired immunodeficiency, 1 in a case of chronic diarrhoea with atrophic villi and 2 in dyspeptic patients. Giardiasis, therefore, cannot be regarded as a cause of non-ulcer dyspepsia, and a systematic search for the parasite is of little interest in such cases. However, giardiasis remains a cosmopolitan parasitic disease with a non-negligible prevalence in France among subjects at risk, such as communities, children, travellers, homosexuals and immunodeficient patients.