1. Some of the basic functional features of the mouse paw eccrine sweat gland were delineated to allow comparison with those of transgenic mice in the future. 2. The mouse sweat secretory coil responds to methacholine, elaborating a K(+)-rich (> 120 mmol/l), Na(+)-poor (< 70 mmol/l) primary fluid as does the rat paw sweat gland, as previously reported. The methacholine-induced sweat rate increases with age in parallel with the growth of the sweat gland over the first 6 weeks of life. 3. The sweating response to cyclic AMP-elevating agents, such as isoprenaline or forskolin, is as much as 40% of the methacholine-induced sweat rate at 1 week of age, but falls to 10% by 6 weeks of age despite the fact that the agonist-induced tissue accumulation of cyclic AMP expressed on a per microgram of protein basis triples with age over the same period. 4. A marked K+ outflux was also noted in response to methacholine and a small K+ outflux was seen in response to cyclic AMP-elevating agonists in superfused adult mouse secretory coils in vitro. 5. Since sweat secretion is usually associated with activation of either K+ channels or Cl- channels or both, and since the sweating occurred in response to cyclic AMP-elevating agonists, we speculate that the cyclic AMP-activated Cl- channels (the mouse version of the cystic fibrosis transmembrane conductance regulator) may also occur in the mouse sweat gland, but that the degree of their expression may be influenced by the age of the mice.