Hydrogen-bonds play a crucial role in determining the specificity of ligand binding. Their important contribution is explicitly incorporated into a computational method, called GRID, which has been designed to detect energetically favourable ligand binding sites on a chosen target molecule of known structure. An empirical energy function consisting of a Lennard-Jones, an electrostatic and a hydrogen-bonding term is employed. The latter term is found to be necessary because spherically symmetric atom-centred forces alone may not adequately reproduce the geometry of two interacting molecules. The hydrogen-bonding term is dependent on the length and orientation of the hydrogen-bond. Its functional form also varies according to the chemical nature of both the hydrogen-bond donor and acceptor atoms, and has been modelled to fit experimental observations of crystal structures. The mobility of the hydrogen-bonding hydrogens is considered analytically in calculating the hydrogen-bond energy. The hydrogen-bonding energy functions will be described and their application will be demonstrated on molecules of pharmacological interest where hydrogen-bonds influence the binding of ligands.