Your TechTool Pro serial number can be found inside your TechTool Pro manual cover or under the "About TechTool Pro" menu when you're in the application. With the release of TechTool Pro 6 we have moved to a new registration system, so if you previously registered your software with Micromat (thank you) your info is not readily accessible to you. We suggest you check your manual cover and within the application first, or re-register during your upgrade purchase process, before contacting us.