Seventeen infants under 2 months of age are described who presented with methaemoglobinaemia and acute diarrhoea during a period of 2 years. No infants beyond this age presented with such characteristics. In none of them was one of the known mechanisms of methaemoglobin formation found. All infants recovered with conventional therapy. Methacmoglobin associated with diarrhoea relapsed in three infants before they were 2 months old. Twenty-six similar cases have been reported in the literature. The mechanism of methaemoglobinaemia in these infants is unclear.