It is shown that quantum-mechanical descriptors obtained as parameters from the one-dimensional radial distribution function of electron momentum can be used to predict molecular activities or properties to a precision that compares favorably with the more traditional QSAR/QSPR methods. The distribution function is derived from momentum space ab initio wave functions. The predictive value of the descriptors is illustrated by their application to the estimation of McGowan's volume, gas-chromatographic retention time, gas−hexadecane partition coefficient, second hyperpolarizability, and tadpole narcotic activity.