From the sulphur-dependent, anaerobically grown archaebacterium Sulfolobus ambivalens Caldariella quinone, CQ-6(12H) and the new Sulfolobus quinone SQ-6(12H), 6-(3,7,11,15,19,23-hexamethyltetracosyl)-5-methyl-benz[b]thioph en-4, 7-quinone have been isolated as main components. Lower homologues SQ-5-(10H), SQ-4(8H), SQ-3(6H), phylloquinone-like species CQ-6(10H), SQ-6(10H) and the menaquinone MK-6(12H) are present as minor components. The results are compared with those from Sulfolobus acidocaldarius. Thermococcus celer, Desulfurococcus mucosus and Desulfurococcus mobilis do not contain quinones in comparable amounts.