Facebook.com/Chicago.OfficialChicago and The Doobie Brothers kick off a joint tour Wednesday night in Tucson, Arizona; the two bands will be on the road together through September.  This particular tour promises to be a bit more collaborative than a regular double bill, however, because both acts actually are planning to perform together on stage simultaneously.

"The Doobies will play a set, Chicago will play a set and then both bands will come onstage and play a third set together," Chicago singer and keyboardist Robert Lamm tells ABC News Radio.  Noting that this will be the third time the two veteran acts have hit the road together, Lamm says, "It's just a ball for me to sing their songs and it's just a wonderful event for fans of music, 'cause you know every single song."

Lamm isn't kidding: between them, The Doobies and Chicago have racked up more than 50 Top 40 singles, including respective #1 hits like "Black Water" and "If You Leave Me Now."

Lamm says the bands' shared history means they have similar fan bases as well, and that makes for a great tour.  "We ****** with The Doobies in the '70s when they first emerged," he remembers.  "They were on the bill with us, with Steely Dan and we did a baseball stadium tour, I think in 1974.  So, we have this great history with the Doobies, and the audience for both Chicago and the Doobies just remains large, and they still love the music."

In addition to Chicago and The Doobies interacting with each other on stage during the tour, fans can also get into the act.  For the third straight year, Chicago will invite one lucky fan on stage each night to sing "If You Leave Me Now." 

This once-in-a lifetime opportunity is part of a joint promotion with the American Cancer Society to raise money to fight breast cancer.  Fans in each city Chicago plans to visit can bid on a meet-and-greet package that includes two premium tickets and a shot at singing on stage with the band.  More details at ChicagoTheBand.com.

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