The following observations were made on collections of sweat from 197 subjects without evidence of disease related to cystic fibrosis of the pancreas after production of localized sweating on the forearm by a standard pilocarpine iontophoresis procedure: 1. Sodium concentrations averaged less than 20 meq/l in children under 11 years of age, while in adults the average concentration rose to 45 meq/l. Sodium concentrations were less variable in children than in adults. Age variation in sodium concentration did not depend upon variation in the rate of sweating. 2. The average potassium concentration in all children and adult females was 11 meq/l. It was lower, 7 meq/l, in adult males. 3. Other sex differences, observed only in adults, were the higher rates of sweating and slightly higher sodium concentrations found in males. 4. Rates of sweating measured in children under 1 year of age were considerably more variable than those induced in older children or adults.
Comparison of these data with observations from 34 children with cystic fibrosis revealed the following facts: 1. Children with this disease always had higher sodium concentrations than pre-pubertal control subjects. Twenty-nine per cent of adult control subjects had concentrations within the cystic fibrosis range. 2. Children with cystic fibrosis had a higher average potassium concentration, 15.0 meq/l, than control children. 3. No sex differences were observed within this group, and the same increased variability in rates of sweating induced in control infants was noted in infants with the disease.
Observations on 53 parents and 18 siblings of the children with cystic fibrosis did not reveal any differences from control subjects of the same age. It was concluded that age, sex, and the presence of cystic fibrosis have a profound effect on the composition of sweat obtained after pilocarpine iontophoresis.