The bioavailability of oral, sublingual, and chewable tablets of erythrityl tetranitrate (ETN) was evaluated in 15 normal men. In a randomized, complete crossover investigation with nitroglycerin and placebo controls, drug‐induced changes in the diastolic amplitude response intensity were measured with a digital plethysmogram. Values for area under the response intensity curve (AUC), maximum response intensity (Imax), and time lapse from dosing to peak response (tmax) were obtained by computer processing and converted to intensity values and AUC segments for specific time intervals. Sublingual nitroglycerin induced a response (p<0.05) from placebo within the first hour. Although somewhat slower in reaching peak intensity, all forms of ETN induced significant responses over placebo (p<0.05) for 2 hr, with oral (swallowed) ETN different for 6 hr. Our results indicate that all the ETN dosage forms were bioavailable, with the longest duration of effect by the oral form.Clinical Pharmacology and Therapeutics(1981)29,35–39; doi:10.1038/clpt.19