Correctly folded into the respective native 3D structure, RNA and DNA are responsible for uncountable key functions in any viable organism. In order to exert their function, metal ion cofactors are closely involved in folding, structure formation and, e.g. in ribozymes, also the catalytic mechanism. The database MINAS, Metal Ions in Nucleic AcidS (http://www.minas.uzh.ch), compiles the detailed information on innersphere, outersphere and larger coordination environment of > 70 000 metal ions of 36 elements found in > 2000 structures of nucleic acids contained today in the PDB and NDB. MINAS is updated monthly with new structures and offers a multitude of search functions, e.g. the kind of metal ion, metal-ligand distance, innersphere and outersphere ligands defined by element or functional group, residue, experimental method, as well as PDB entry-related information. The results of each search can be saved individually for later use with so-called miniPDB files containing the respective metal ion together with the coordination environment within a 15 A radius. MINAS thus offers a unique way to explore the coordination geometries and ligands of metal ions together with the respective binding pockets in nucleic acids.