In the context of reconsidering the Quantitative Structure-Activity Relationship (QSAR) methods
at the economical level, namely the optimization rules of OECD, the present review unfolds the key features
of Minimal Sterical, Monte-Carlo and Minimal Topological Difference (MTD) methods, developed for
quantitative treatment of the relations between biological activity of organic chemical compounds (drugs,
pesticides, and so on) and their structures. The initial Minimal Steric Difference (MSD) is completed by the
three-dimensional variant of the MTD method, being the last one referred to here, while the main principles
of validating and guiding a viable QSAR method verified by the analytical-automated MTD, thus enlarging
the perspectives of understanding the chemical-biological interaction at the level of ligand-receptor sites,
cavity, and walls, with a true service to the future adaptive molecular design.