Using data from the literature, a method is adopted for determining the empirical composition and the unit carbon formula for dried Escherichia coli K-12 cells by summing the quantities of C, H, 0, N, P, and S in each of the major classes of macromolecular substances comprising the cellular biomass. With these data and the molar growth yield of cells on succinic acid, equations are written representing the anabolism and catabolism of E. coli K-12 on this quantity of substrate. The enthalpy change accompanying catabolism can be calculated directly using standard enthalpies of formation because there is no term representing cellular substance. The enthalpy change accompanying anabolism is calculated to be very small or zero using microcalorimetric and other data from which the enthalpy of formation of a unit quantity of living cellular substance can be obtained. This indicates that the net enthalpy change accompanying the growth process (anabolism plus catabolism) is the same as that calculated for catabolism alone, in agreement with the same conclusion by several investigators using direct microcalorimetry. The method described here of determining the unit carbon formula and the quantity of ash remaining after cellular combustion is compared to that conventionally used in which cellular P and S is considered either to be negligible or to be a part of the ash. It is concluded that equations representing anabolism and the growth process can be written more accurately using the presently described method, leading to more accurate thermodynamic calculations.