A gas-liquid chromatographic method for the quantitative determination of hopanoids with an elongated side chain was developed. After extraction of lipids from Bacillus acidocaldarius, periodate oxidation, reduction and acetylation the 1-hydroxyethane-29-hopane acetate was quantitated by comparison with 1-octadecanyl-glycerol ether. The contents of extended hopanoids increased strongly with increasing temperature and moderately with decreasing pH. Hopene showed no significant alteration with temperature and pH.