The percutaneous resorption of mercury (mercuric phenylborate, mercuric oxycianide and white precipitate ointment) has been investigated in 25 patients by measuring the urinary excretion of mercury. No significantly raised values were found after application of mercury on large areas of the body over several days. Only in one patient with a disturbed renal function was there an increase in the excreted mercury. The question is discussed how far one is allowed to draw conclusions on percutaneous resorption of mercury on the basis of the urinary excretion.