From the archaebacterium Thermoproteus tenax, strain Kra-1 a mixture of 6 quinones of menaquinone and phylloquinone type with isopentyl side chains, MK-6(12H), MK-6-(10H), MK-5(10H), MK-5(8H), MK-4(8H), MK-4(6H) and two analogous quinones, containing in addition a methyl group in the naphthoquinone system, were isolated and characterized.