How to determine sub-lethal dose? - (Jan/16/2013 )

Hello folks,

I need help with determination of sub-lethal dose for proliferation assay!
I perfomed MTS assay using concentration series of a substance in my cells. Which dose should I use for proliferation & migration assay? Is there any rule to be used?

-attached MTS assay-

THX

You could use anything that doesn't cause any death...