Antibody-like selectivities are introduced into man-made polymeric systems by means of molecular imprinting. On the molecular scale, organic contaminants in water were analysed by 10 MHz QCM sensors coated both with affinity layers and with selective imprinted polymers. Affinity layers, polystyrene/silicone, yield sensor effects for aromatic hydrocarbons according to, e.g., molecular weight and solubilities, a prediction by molecular modelling is proposed. Imprinted layers, however, recognise molecular shapes: the lean toluene is favoured by factor of six to the more bulky o-xylene; even the three xylenes can be distinguished from each other. On the micrometre scale, erythrocytes of different blood groups are differentiated, although their geometrical shape is identical. In this case, the recognition is accomplished by a predefined hydrogen bonding network between excess OH groups of the polyurethane layer and the sugar molecules on the cell surface defining the blood group.