In August 1998, a large outbreak of gastroenteritis occurred in a Swiss village of 3500 inhabitants whereof more than 50% were affected. A high contamination of drinking water with faecal coliforms revealed a defect in the waste water system. The objective of the present study was to investigate the outbreak in respect of the presence of human pathogenic viruses. Drinking water and clinical samples from patients were examined for the presence of 'Norwalk-like viruses' (NLVs) and enteroviruses. NLVs and enteroviruses were detected by reverse transcription-polymerase chain reaction (RT-PCR) in one of two drinking water samples. Five of seven stool samples from ill persons were positive for NLVs. Typing of NLV-specific RT-PCR products by DNA sequencing revealed the presence of an identical genogroup-1 strain closely related to Southampton virus in both the water and one of the stool samples. A genogroup-2 NLV strain was identified in all positive stool samples. The enteroviral amplicon showed high sequence similarity with swine vesicular disease virus. These results demonstrate that the drinking water was highly contaminated with enteric viruses and that at least two NLV strains were involved in this outbreak of gastroenteritis.