With the US Food and Drug Administration’s recent label change of warfarin to include genetic testing for warfarin sensitivity, manufacturers are developing assays, and laboratories are offering testing. This article describes the genetic variants for which testing is available. Current technologies and assays are compared, including considerations for laboratories in choosing a method. Finally, laboratory issues that apply to all methods, such as quality control and proficiency testing as well as service issues including turn-around-time requirements are discussed.