PASADENA, Calif. (AP) -- Reality shows like ''Big Brother,'' in which one contestant pulled a knife on another, are risky but represent an effort to try something different, CBS executives said Tuesday.

''I'm tired of putting on 'Diagnosis Murder' reruns in the summer. There's a quest to put on new forms of programming,'' CBS President Leslie Moonves told the Television Critics Association.

Under sharp questioning, Moonves said the network believes ''Big Brother'' is worthwhile but does require vigilance.

Source: AP Entertainment