Promoting the integrity of horse racing and maintaining a “level playing field” for owners, trainers, and horses is a major ongoing commitment for racing jurisdictions around the world. A great deal of time and resources is spent by racing commissions and tracks to ensure compliance with the rules of racing. Drug testing and blood gas testing for evidence of “milkshakes” (alkalinizing compounds) are two of the better known methods of encouraging equitable racing, but many horse owners and trainers do not fully understand the fundamentals of testing for these different classes of illegal substances. The purpose of this article is to present, in a question and answer format using simple language, the elementary facts of blood gas testing and to compare and contrast blood gas testing to the testing for illegal drugs. A better comprehension of blood gas testing may help owners and trainers to better understand the rules related to “the black box.”