<p>The structures of metabolic products of echinochrome, the substance of the medicine histochrome, were established by high-resolution GC-MS using a deuterium label. Their structures were compared with those of the metabolic products of its inactive trimethyl ether. This suggested that the cardioprotective activity of the histochrome drug could be determined by echinochrome, its 2(3)-methoxy derivatives, their monoglucuronides, and (trihydroxyethyl)naphthoquinonyl urea. The research significantly narrowed the list of metabolites responsible for the biological properties of histochrome drug.</p>