<jats:p>Novel tertiary branched tetra-amines, quaternary branched penta-amines, linear penta-amines and linear hexa-amines were distributed as the major polyamines in six obligately extremely thermophilic eubacteria belonging to Thermoleophilum, Bacillus or Hydrogenobacter. The major polyamine of Thermoleophilum album and Thermoleophilum minutum was identified as a quaternary branched penta-amine, 4,4-bis(3-aminopropyl)-1,8-diamino-4-azaoctane (NH2[CH2]3N+([CH2]3NH2)2[CH2]4NH2) by h.p.l.c., t.l.c. and g.c.-m.s. Hydrogenobacter thermophilus and Hydrogenobacter halophilus contained another quaternary branched penta-amine, 4,4-bis(3-aminopropyl)-1,7-diamino-4-azaheptane (NH2[CH2]3N([CH2]3NH2)2[CH2]3NH2) as the major polyamine, and tertiary branched tetra-amines (4-(3-aminopropyl)-1,7-diamino-4-azaheptane (NH2[CH2]3N([CH2]3NH2)[CH2]3NH2), 4-(3-aminopropyl)-1,8-diamino-4-azaoctane (NH2[CH2]3N([CH2]3NH2)[CH2]4NH2)) and 4,4-bis(3-aminopropyl)-1,8-diamino-4-azaoctane were confirmed as minor components. Bacillus schlegelii contained a branched tetra-amine, 4-(3-aminopropyl)-1,8-diamino-4-azaoctane, a branched penta-amine, 4,4-bis(3-aminopropyl)-1,8-diamino-4-azaoctane, a linear penta-amine, 1,16-diamino-4,8,13-triazahexadecane (NH2[CH2]3NH[CH2]3NH[CH2]4NH[CH2]3NH2) and linear hexa-amine(s), 1,20-diamino-4,8,12,17-tetra-azaeicosane (NH2[CH2]3NH[CH2]3NH[CH2]3NH[CH2]4NH[CH2]3NH2) and/or 1,20-diamino-4,8,13,17-tetra-azaeicosane (NH2[CH2]3NH[CH2]3NH[CH2]4NH[CH2]3NH[CH2]3NH2).