>Hi,
>What if the mock BO need to be passed or called by another BO? .NET will still referring to the method of type specified instead of new keyword one.

Hi,
I'm not sure I understand what you are asking - it sounds as if you want existing calls to the base class methods from other parts of the framework to be transparently diverted to a method in a sub-class. AFAIK that's not doable. I also don't see how having the base class method marked as virtual would have helped in that situation in the first place?
Regards,
Viv