Gener verification in sports (also sometimes loosely referred to as Sex determination) is the issue of verifying the eligibility of an athlete to compete in a sporting event that is limited to a single gender. The issue arose a number of times in the Olympic games where it was alleged that male athletes attempted to compete as women in order to win, or that a natural intersex competed as a woman. Sex testing began at the 1966 European Track and Field Championships in response to suspicion that several of the best women athletes from Soviet Union and Eastern Europe were actually men. At the Olympics, testing was introduced in 1968 at the Mexico City games. While it arose primarily from the Olympic games, sex determination affects any sporting event. However it appears it most often becomes an issue in elite international competition.