Major League Baseball and the players' union have agreed to expand their drug program to include random in-season blood testing for human growth hormone and a new test for testosterone, they said on Thursday.

The advanced testing will start this season, in what will be the sternest doping program in major North American professional sports.

"This agreement addresses critical drug issues and symbolizes Major League Baseball's continued vigilance against synthetic human growth hormone, testosterone and other performance-enhancing substances," MLB commissioner Bud Selig said in a statement.