From Michael S. Schmidt at the New York Times:

Major League Baseball is investigating the accuracy of statements by Alex Rodriguez about his use of performance-enhancing drugs, according to people within baseball who were briefed on the matter.

Investigators have contacted several of Rodriguez’s associates to determine whether he used performance-enhancing drugs for a longer time than he has admitted, the people said.

Schmidt's sources say that the investigation was initiated in early March, after A-Rod met with investigators. Selena Roberts, the author of the upcoming "A-Rod" book, was contacted and declined participation, due to journalistic conflicts.

Via John Schlegel.