The effect of isosorbide 2-mononitrate (IS-2-MN) was compared with that of isosorbide dinitrate (ISDN) in rats regarding the antianginal, haemodynamic and pharmacokinetic properties. The antianginal effect of IS-2-MN in equal oral dose persisted 3 times longer in the rat than did ISDN. In the same oral dosage, the two compounds caused the equal reduction of the number of deaths after an acute myocardial infarction. The intravenous or enteral administration of a single IS-2-MN dose caused an increasingly dose-dependent reduction of the systolic and mean arterial blood pressure in anaesthetized rats. The amounts of IS-2-MN required for the purpose were identical for both kinds of application. The fall of the systolic and mean arterial blood pressure due to ISDN is approx. 22 times weaker after enteral administration than it is after intravenous application. The hypotensive effect of ISDN or IS-2-MN could be antagonized by pre-treatment of the animals with i.v. dihydroergotamine (DHE). The half-life of IS-2-MN in the rat was unchanged after increase of the oral doses. The bioavailability of IS-2-MN in the rat was 100%. 1 h after oral or intravenous administration of IS-2-MN to the rat, the concentrations in the walls of aorta abdominalis and aorta thoracica and in the walls of vena cava caudalis and vena thoracica were distinctly greater than in the blood or in the other tissues examined.