I know that you subtract for legal lending limit purposes the amount fully secured by a certificate of deposit. However, if the loan is participated, can you subtract the entire portion of the CD from your own legal lending limit or do you have to pro-rate the amount of the CD between the participating banks? For example, if the loan is 50% participated do you only get to subtract 50% of the CD? Any thoughts or experiences would be helpful.

You need to read your participation agreement. Since the loan is not 100% collateralized by the CD, the agreement should state how the collateral will be divided in the event of default.