Four models taken from the literature, which permit calcn. of heats of combustion from elemental anal., are evaluated from a theor. point of view. In order to obtain exptl. values of heat of combustion with a higher degree of accuracy than that in the literature, an improved sample prepn. technique based on lyophilization of microbial biomass was developed. Heat of combustion was detd. by direct measurement in a calorimeter and compared to calcd. values from each of the literature models. Giese's formula predicted heat of combustion the most accurately. The enthalpy content of the bacteria investigated (23.13 kJ/g) significantly differs from that of yeasts (21.21 kJ/g). [on SciFinder (R)]