Cellular polyamines of 25 newly validated thermophilic, acidophilic, alkaliphilic or radio-resistant bacteria (eubacteria) and 35 methanogenic, thermophilic or extremely halophilic archaea (archaebacteria) were analyzed by HPLC and GC. In the domain Bacteria, quaternary branched penta-amines, N⁴-bis(aminopropyl) norspermidine and/or N⁴-bis (aminopropyl)spermidine, were detected in the extreme thermophiles, Hydrogenovirga and Thermodesulfidibacter of the phylum Aquificae and Thermus of the phylum Thermus-Deinococcus. A liner penta-amine, homocaldopentamine, was found in moderately thermophilic Thermodesulfovibrio. Spermine, a tetra-amine, was found in the moderate thermophiles, Meiothermus, Exilispira, Desulfurispora, Desulfotomaculum, Caloramator and Calditerrivibrio but not in slightly thermophilc Thiofava and mesophilic radio-resistant Deinococcus. An acidophilic slight thermophile, Acidimicrobium, contained only cadaverine as a novel polyamine profile. The occurrence of spermine in mesophilic Acanthopleuribacter belonging to the phylum Acidobacteria was a unique profile. Alkaliphilic Alkalibacterium species were devoid of cellular polyamines. In the phylum Euryarchaeota of the domain Archaea, the branched penta-amines were distributed in the extremely thermophilic genera, Methanocaldococcus, Archaeoglobus and Thermococcus but not in hyperthermophilic Methanopyrus as well as in the mesophilic genera, Methanobacterium, Methanosaeta, Methanolobus, Methanocella and Methanofollis. Some methanogenic mesophiles contained spermine. Long and branched polyamines were not found in 23 extreme halophiles and halalkaliphiles belonging to the order Halobacteriales.