A group of older children with galactosaemia, whose ability to metabolize galactose was reviewed, showed grossly impaired ability to deal with an isolated galactose load. Blood glucose levels were slightly lower in the children with galactosaemia, both in the fasting state and after galactose ingestion, than in their heterozygous relatives or in controls: this phenomenon does not appear to be the result of excessive insulin secretion in the galactosaemic patients. Surprisingly, glucosuria occurred in 7 out of 8 galactosaemics and one out of 13 carriers during a tolerance test. In the absence of definite knowledge as to whether an elevated, though asymptomatic level of blood galactose may in the long‐term damage brain, lens, liver or other tissues, it is suggested that galactosaemic patients should maintain a low‐galactose diet as a lifelong pol