The clinical laboratory forms an essential bridge between fundamental discoveries in biological sciences and their transition into effective medical practice. The genetic basis for individuality in drug metabolism and response is the result of a finite number of inherited sequence variants (alleles) of genes encoding drug-metabolizing enzymes and drug receptors. Pharmacogenetics (PG) links differences in gene structure with pharmacological differences in pharmacokinetics and pharmacodynamics. The next step in the process of applying PG (or pharmacogenomic) information to individualized therapeutic management is dissemination of this information to practicing physicians by clinical laboratorians. Transitioning PG analysis into clinical practice will require professionals in laboratory medicine to identify relevant polymorphisms, develop sensitive and specific testing strategies, and, in conjunction with physicians and pharmacologists, communicate interpretive guidelines regarding appropriate indications for testing and rational dose adjustment. We review these concepts and provide examples of how PG can be applied to support therapeutic decision making.