The design of new potential drugs is traditionally the domain of the pharmacochemist. In the last decades Quantitative Structure-Activity Relationship (QSAR)-techniques are used more and more to define the 'essential' moieties of a pharmacon. A logical evolution in the search for the relation between the 3D-structure of drugs & their biological activity is the 3D-structure analysis of the biological target molecules and the receptor- ligand interaction. Our aim is, starting from experimentally determined crystal structures of drugmolecules and proteins to model via molecular modelling techniques the recognition and interaction area between pharmacon and receptor and to evaluate eventuel conformational changes. In particular attention is given to the structure-activity relationships of Ca channel blockers belonging to different chemical structures and of modified 2',3'-dideoxypyrimidine nucleosides and of pyranosyl nucleosides. Between the proteins with therapeutic relevance 3D-structure analysis is going on on steroid binding proteins (vitamin-D binding protein (DBP), cellular signaling proteins, phosphoserine phosphatase (PSP), Phosphomannomutase (PMM), Peroxisome targeting signal receptor (PEX5p). Also a plant R Naselike protein and plant lectins are under study. Co-crystallization studies between the some proteins and their most relevant ligands is in progress.