Abstract A new measure of the interaction between two molecular fragments, contact intensity (ContI), is defined as the ratio X /( Y + Z ), where X is the average inter-fragment inter-atomic distance and Y and Z are the average intra-fragment inter-atomic distances. Its prominent advantages, relative to alternatives, are the following: ContI does not need a priori assumptions or parameterization and it is intrinsically standardized, to take into account the variability of shape and dimension amongst different molecular moieties. The reliability of ContI is demonstrated by the fact that it allows one to well describe fundamental properties of globular proteins.