1. Various drugs of neuropsychopharmacological importance contain one or more chiral centres, or centres of asymmetry are introduced during drug metabolism. 2. A drug or drug metabolite with one asymmetric centre exists in two enantiomeric forms, of which usually only one possesses the desired pharmacological activity. The other enantiomer may be inert, or possess an undesired activity. 3. In certain circumstances it is appropriate to administer the racemic drug (mixture of enantiomers), while on other occasions only the pure enantiomer which possesses the desired activity should be given. 4. Drugs employed in psychiatry that contain centres of asymmetry, or are metabolized to pharmacologically active chiral products are identified and implications of chirality are discussed.