Is there a parameter that will exclude return sales order quantities from the calculations in MRP?

Thanks.

There is no such parameter...

However you can receive the returns in a non-nettable warehouse (or in a warehouse for which 'include in EP' is not selected) and the EP/MRP will ignore all the items in such warehouse in EP/MRP

Okay ... thanks ... the problem here is that they keep an unbelievable amount of return orders open - many a year old. They have been pushing the dates out on them to keep them out of MRP.