VOIDOO is a program for detection of cavities in macromolecular structures. It uses an algorithm that makes it possible to detect even certain types of cavities that are connected to "the outside world". Three different types of cavity can be handled by VOIDOO: Vanderwaals cavities (the complement of the molecular Vanderwaals surface), probe-accessible cavities (the cavity volume that can be occupied by the centres of probe atoms) and MS-like probe-occupied cavities (the volume that can be occupied by probe atoms, i.e. including their radii). 

VOIDOO can be used for: detecting and delineating cavities; measuring cavity volumes and molecular volumes; identifying non-protein atoms inside cavities; identifying protein atoms that line the surface of cavities; producing display files for O for visualising cavities; producing macro files for O to display (1) non-protein residues (ligands, solvent molecules) that are situated inside each cavity, and (2) protein residues that surround each cavity; producing display files for O for visualising molecular surfaces; (randomly) rotating molecules for assessing the accuracy of cavity volumes (by repeated calculations using differently oriented copies of a molecule).