Three nitrogen-fixing bacteria, Azotobacter vinelandii, Beijerinckia indica and Beijerinckia mobilis, were shown to contain large amounts of triterpenoids of the hopane series. In A. vinelandii, the major compound was a novel bacteriohopanepentol ether accompanied by a similar bacteriohopanetetrol derivative: in both compounds, the hopanoids are linked via an ether bond to a carbapseudopentose moiety often found in bacterial hopanoids. In the two Beijerinckia species, diplopterol and 2β-methyldiplopterol were accumulated in much larger amounts than those usually recorded in hopanoid-producing eubacteria, while 2β-methyldiploptene was isolated for the first time from B. mobilis. Whereas in B. mobilis aminobacteriohopanetriol was the only C35 hopanoid, the simultaneous presence of bacteriohopanetetrol and aminobacteriohopanetriol in B. indica is a rather unusual feature.