PDBlib is an extensible object oriented class library, written in C++ for representing the 3-dimensional structure of biological macromolecules. The library models the structural features of proteins,DNA,RNA and complexes thereof, at a level of detail on a par with which can be parsed from a Brookhaven Protein Data Bank (PDB) entry. However, the memory resident representation of the macromolecule is independant of the PDB entry, and can be obtained from other sources such as relational, and object-oriented databases.