SynopsisThe method of Minor to visualize by iodine–starch–reaction the activity of sweat glands was used in combination with image‐analysis to quantify sweat‐secretion. Aqueous aluminium chlorohydrate solutions (ACH) (1, 2, 4, 8, 16%) were applied twice daily for 6 days to defined areas of the lower volar forearms. After 3 and 6 days of treatment perspiration was induced by thermal stress. The dark blue spots on top of active glands which are formed by iodine–starch–complexes were counted and their projection area was measured by an image analysing system. Increasing concentrations of ACH lower the number of active sweat glands, while the size of the dark spots is not dependent on the concentration of the active