Abstract The delivery rate of etidronate disodium (EHDP) to a pig from an iontophoretic device placed on its back has been determined by comparing the plasma levels and amount on bone with the values obtained following an intravenous dose. A 5-cm 2 iontophoretic patch containing 9.8% EHDP and operating at a current level of 4 mA delivered approximately 2 mg of drug in 1.1 hours. The peak plasma level resulting from this treatment was only 1.7% of that obtained from the intravenous infusion (6 mg). Elimination kinetics of the drug after cessation of the treatment paralleled those obtained in the intravenous study. The amount of drug delivered was consistent with a prediction based on iontophoretic transport of EHDP through skin in vitro.