Def Leppard are getting ready for their 11-show Viva Hysteria residency in Las Vegas starting next month -- and it's been challenging.

Singer Joe Elliott tells us they're having production meetings, and guitarists Phil Collen and Vivian Campbell, in Los Angeles where they both live, have been going over the songs from Hysteria that they haven't played live in a long time -- including some Campbell has never played. Elliott says he's also getting himself ready and later this month he'll "start going hardcore by rehearsing on my own. I can do a lot of donkey work."

Viva Hysteria runs from March 22nd through April 13th at The Joint at the Hard Rock Hotel and Casino.