via press release:
"STAR TREK" ICON LEONARD NIMOY BEAMS UP TO "THE BIG BANG THEORY"
Feb. 29, 2012 - It's a dream come true for Sheldon when he has a close encounter with his hero, Mr. Spock, on THE BIG BANG THEORY, Thursday, March 29 (8:00-8:31 PM, ET/PT) on the CBS Television Network. Legendary sci-fi icon Leonard Nimoy guest stars, lending his voice to a unique reprisal of his three-time Emmy-nominated "Star Trek" role.
"Leonard Nimoy's first appearance on BIG BANG was as DNA on a napkin," stated Executive Producer Bill Prady. "For this episode, we are delighted to hear his voice. We look forward to introducing Mr. Nimoy, body part by body part, over the course of many seasons to come."
Currently in its fifth season, THE BIG BANG THEORY, airs Thursdays at 8:00 PM, ET/PT on CBS. The Emmy and Golden Globe-nominated series was created by Chuck Lorre and Bill Prady, who serve as executive producers along with Steven Molaro.