In 6 healthy volunteers, intravenous infusions of nitroglycerin 4.8 and 10.6 micrograms/min yielded mean steady-state plasma concentrations of 0.5 +/- 0.02 and 0.82 +/- 0.04 ng/ml as determined by a gas chromatographic/mass spectrometric method. The plasma concentrations reached in the same subjects 17 h after application of Nitroderm TTS 5 and 10 with in vivo release rates of 3.7 and 5.7 micrograms/min were 0.28 +/- 0.01 and 0.37 +/- 0.01 ng/ml, respectively. Thus, 75% of the quantity of nitroglycerin released by the systems passed into the circulation. The inter-individual and intra-individual variations in plasma concentrations were similar for both modes of administration. The nitroglycerin-induced morphological changes in the fingerpulse wave were clearly dose-dependent, but it seems that this pharmacodynamic parameter is determined less by the plasma concentration than by the nitroglycerin content of the vascular wall.