Nitroglycerin plasma concentrations following transdermal application were measured in nine healthy subjects during supine rest position or during supine rest interrupted by sitting or exercising for 20 min. Sitting led to almost doubling of the average plasma concentrations (0.31 ng ml-1 before sitting, 0.55 ng ml-1 at the end of the sitting period), but exercise was accompanied by a much more marked increase in average plasma concentrations, which reached its maximum 5 min after ending exercise (0.22 ng ml-1 before exercise, 1.26 ng ml-1 5 min after the exercise period). Changes of bioavailability as well as of systemic clearance might be involved in the exercise-induced increase in plasma nitroglycerin concentrations.