The default parameter passing style for ILE RPG is to pass by reference. Consequently, you do not have to code any keywords on the parameter definition to pass the parameter by reference. You should pass parameters by reference to a procedure when you expect the callee to modify the field passed. You may also want to pass by reference to improve run-time performance, for example, when passing large character fields. Note also that parameters that are passed on external program calls can only be passed by reference.