AbstractThe synthesis is described of 2‐methyl‐4‐aminonaphthol‐1 hydrochloride and of 2‐methyl‐1,4‐diaminonaphthalene dihydrochloride, both water soluble compounds possessing a high vitamin K activity. For the first mentioned substance this has already been reported by Emmett, Kamm and Sharp1), and in America the compound has been termed vitamin K5.In this communication we prove for the first time the high activity of 2‐methyl‐1,4‐diaminonaphthalene dihydrochloride, for which we propose the name vitamin K6. Information is given about the stability, toxicity and clinical value of the