Since 1968, tap water iontophoresis has been employed as the method of choice for treating palmoplantar hyperhidrosis. Special electrodes also allow treatment of axillary hyperhidrosis. Tap water iontophoresis also can extend symptom -free intervals in dyshidrotic palmar eczema. The mechanism action is most likely a functional disturbance of the secretory mechanism of eccrine acini. During the induction phase, treatments are carried out once daily. Current direction may be switched before each treatment or, even better, kept constant until one side, preferably the dominant hand on the anode, is sweating normally. Then polarity is switched until both hands are adequately treated. During the weekly maintenance therapy, current direction is switched before each treatment. The most comfortable means of iontophoretic treatment employs pulsed direct current of high frequency (5-10 kHz) which is better tolerated than continuous direct current and also suitable for children. Side effects are minimal and transient. Only slight skin irritation or sensations of discomfort may occur during treatment. Electric burns and shocks can be avoided by following routine precautions. Contraindications for tap water iontophoresis are metallic implants, such as cardiac pacemakers, or orthopaedic joint or bone implants, if they are within the electric circuit. Defects in the skin barrier, which can not be protected by petrolatum or insulating tape, also represent a temporary contraindication. Treatment in pregnancy is contraindicated, since experience is lacking.