To ensure toxicologically the potential antiarrhythmic agent 3-carbethoxyamino-5-dimethylamino-acetyl-10,11-dihydro-dibenz[b,f] azepine hydrochloride (Bonnecor, GS 015, AWD 19-166), the following preclinical studies have been made up to the present: Determination of the acute toxicity on mice and rats, toxicity test on the rat by repeated applications, study as to the action of GS 015 on the prenatal development of the rat, diverse toxicologic studies on reproduction, mutagenity tests by using the DNA repair test and the Ames test. The results of these studies are represented in a summarized form. A good tolerance of GS 015 can be derived from the results of the preclinical studies gained up to now.