A number of molecular modeling techniques determine molecular properties by identifying the major low-energy conformations of a molecule or complex and evaluating the configuration integral for each such conformation. The mode integration (MINTA) technique uses normal-mode analysis in the rigid rotor approximation to facilitate evaluation of these configuration integrals in all internal degrees of freedom. This paper analyses the theory underlying MINTA and shows that the method omits numerically important terms related to the Jacobian matrix for the transformation from Cartesian to translation-rotation-vibration coordinates. It is shown that the method can be corrected either by including the missing terms or by changing, to a more convenient coordinate system that does not require use of the rigid rotor approximation and hence is potentially more accurate.