The effect of organic and inorganic nitrovasodilators (sodium nitroprusside; 3-morpholinosydnonimine; glyceryl trinitrate; isosorbide dinitrate; sodium nitrite, was studied on the release of histamine evoked by compound 48/80 and calcium ionophore A 23187 in isolated purified rat serosal mast cells. All the compounds tested were capable of significantly reducing the release of histamine in a concentration-dependent fashion, at different levels of potency. This effect was reverted by oxyhaemoglobin. The inhibitory effect of glyceryl trinitrate on the release of histamine was potentiated in cells taken from animals pretreated with Escherichia coli lipopolysaccharide, and decreased by NG-nitro-L-arginine methyl ester. Glyceryl trinitrate and isosorbide dinitrate concentration-dependently increase the generation of nitric oxide by rat serosal mast cells. The inhibitory effect of glyceryl trinitrate and isosorbide dinitrate on the release of histamine from mast cells was potentiated by N-acetylcysteine, which significantly increases the generation of nitric oxide by mast cells. It is concluded that nitrovasodilators inhibit the release of mast cell histamine through the generation of nitric oxide. The effect may be relevant in considering the perivascular location of mast cells and the role played by these cells in cardiovascular pathophysiology.