The fast Fourier transform of a free-induction decay curve generated by a Fourier operation on a bond distance matrix representation of a molecule gives a frequency domain spectrum that, when plotted as a line of points, is similar to a chromatogram and is called the inverse molecular transform. Within a series of compounds including lower alkanes, alkenes, cyclics, heteroalipathics, and aromatics, the amplitude of the transform ordinates increased directly with the size of the molecule and with going from straight chain to cyclic structures with the same number of carbon atoms. A derived transform index gave a unitary numerical structure descriptor that was used in a topological comparison of structures and is called the transform similarity ratio. With further investigation, this methodology appears to have the potential to generate correlation descriptors, other molecular similarity measures, or an index of protein globularity. © 1993 John Wiley & Sons, Inc.