Seven cases of cystic fibrosis complicated by chronic salt depletion and failure to thrive were studied. After replacement of the salt deficit, the metabolic abnormalities resolved, and weight gain was rapid. This should be considered as a differential diagnosis in children who have been diagnosed as having cystic fibrosis, but who fail to thrive despite standard treatment.Metabolic alkalosis in association with low serum electrolyte concentrations (hyponatraemia, hypokalaemia, and hypochloraemia) is uncommon in infancy. In the United Kingdom the more common causes included pyloric stenosis, gastric drainage without electrolyte replacement, and-less common-chloride losing nephropathy, the use of thiazide diuretics, and Bartter's syndrome. Acute salt loss in cystic fibrosis is well known, but the gradual development of abnormally low serum electrolyte concentrations, metabolic alkalosis, and failure to thrive without severe dehydration is less widely recognised. Though most cases have been reported from North America, the syndrome has also been described in the United Kingdom.

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On 1 March a two year programme began in the United Kingdom of phased transfer of all diabetics requiring insulin to insulin in a strength of 100 units/ml. Factors affecting the absorption of insulin from subcutaneous tissues include site of injection,' exercise,2 dose,3 strength of the insulin, volume, and the patient's age.4 We examined the effect of giving identical doses of soluble insulin in strengths of U-40 (40 units/ml) and U-100 (100 units/ml).