This paper describes the clinical features of six children who developed the haemolytic-uraemic syndrome after treatment with metronidazole. These children were older and were more likely to have undergone recent bowel surgery than are other children with this condition. While the involvement of metronidazole in the aetiology of the haemolytic-uraemic syndrome is not established firmly, the action of this drug in sensitizing tissues to oxidation injury and the reported evidence of oxidation changes in the haemolytic-uraemic syndrome suggest a possible link between metronidazole treatment and some cases of the haemolytic-uraemic syndrome.