In this paper we tested the hypothesis that the building up of model-based methods to correlate molecular structure with the concentration required for the production of some biological effects such as giant cell formation, reduction of the number of viable cells, etc. is possible. We provide data supporting this model presenting structure-relationships results for two sets of molecules displaying inhibitory activity against some effects of HIV-1 and H1N1 viruses. The local atomic reactivity indices were calculated at the ZINDO/1 level of the theory. We found several statistically significant equations showing that some process is charge-, orbital- and/or steric-controlled. The main and most important conclusion is that the method, originally designed only for in vitro molecule-site equilibrium constants, nicely works for other properties like cytopathicity protection and cytostatic concentrations. This opens an entirely new research field and raises the possibility that this methodology be applied to other types of reports of biological activity data. We conjecture that this method is superior to the Hansch approach and that it is related in a still unknown form to the Hammett methodology.