The letter by Sanchez-Bayle et al¹ states that the administration of hypotonic saline to children with gastroenteritis is not, in their view, associated with an increased risk of hyponatraemia. This is in sharp contrast with our findings,[2 3] and those of others, showing that the risk is real. Unfortunately, the data provided by Sanchez-Bayle are insufficient for analysis and we look forward to their findings being published in full. On the other hand, we also concluded from our studies that any isotonic solution used should contain added glucose. In two studies of children with gastroenteritis (n  =  154), we have documented a 4% rate of hypoglycaemia (blood glucose concentration, 2.6 mmol/l) at presentation.[2 3] In both studies, the hypoglycaemia responded to the 2.5% dextrose content of the intravenous fluid prescribed at either a slow or rapid rehydration rate. Much of the recent literature on isotonic versus hypotonic saline solutions for children ignores the need for glucose, and we welcome this focus.