Nitrates are available in the GDR as: Nitrangin liquidum (0.1 mg glycerol trinitrate/gt.) and Nitrangin isis in 0.3 and 0.8 mg capsules for preventing anginal attacks; Trinitrosan (glycerol trinitrate) for intravenous therapy of ischemic conditions and acute left heart failure; Pentalong 50 (50 mg pentaerythrityl tetranitrate, PETN) for long-term oral therapy. PETN was introduced in 1977 as Pentalong (20 mg), and in a sustained-release form as Pentalong longo (40 mg PETN/dragée: 20 mg in a coated core and 20 mg in capsule form). Patients taking Pentalong longo repeatedly reported undissolved coated pills in their feces due to the varying solubility rates of the coating. It was primarily intended that the coating ensure the sustained release of PETN from the core. Although tests confirmed that 90% of the pill did not release the PETN after 180 min in the "in vitro gastric juice" and of these 90%, another 94% had not released the PETN after 30 min in the "in vitro intestinal juice", it could not be determined what percentage of pill cores did later dissolve and release the PETN during passage through the intestines. Clinical tests on pill cores with eight coatings also revealed no predictable breakdown and release of the core contents. This was not the case with pill cores with five layers of coating, used henceforth for obtaining a sustained release effect with Pentalong longo. However, clinical examinations suggested to abandon sustained release formulations because of the high interindividual release of PETN in the gastrointestinal tract from coated dragées and the drug-inherent sustained action of PETN. The corresponding clinical experiments are the subject of this report.