Sweat Na+, K+, H+, Cl-, Ca2+, and protein concentrations were reexamined with the use of three methods; namely, in vitro sweat induction from isolated single sweat glands, intradermal methacholine-induced sweating, and thermally induced sweating. [Na+] and [K+] in the primary sweat induced in vitro were nearly isotonic to the bath in both cystic fibrosis (CF) and control. In CF the [Na+] in both proximal ductal and skin surface sweat was always higher than 100 mmol/L. However, [Na+] never reached the isotonic level of 151 mmol/L, even at the highest sweat rate. Thus Na+ absorption never saturates, suggesting that the net NaCl absorption may increase with increasing sweat rate. pH of the primary sweat was 7.13 for CF and 7.29 for control, which corresponds to a [HCO3-] of 7.3 and 10.5 mmol/L, respectively. [Cl-] in the primary sweat was hypertonic (134 mmol/L for CF and 129 mmol/L for control) to the bath (118.4 mmol/L). In CF, ductal acidification of sweat occurred normally during intradermal methacholine-induced sweating, whereas ductal acidification of sweat was much higher in control than in CF in thermally induced sweating. [K+] in CF was higher in the skin surface sweat but not in the proximal duct sweat, suggesting that the predominant site of K+ secretion in CF may be in the distal duct. [K+] in the intradermal methacholine-induced sweat was much higher than that of thermally induced sweat in both CF and control samples. Free but not total [Ca2+] was also increased in CF skin surface sweat. The sweat protein concentration was the same in both CF and control samples. The mechanisms of the different electrolyte concentrations in CF sweat remain to be studied. However, the present observations will provide the basis for future studies on normal and abnormal regulation of membrane transport in CF sweat glands.