Hi, Sorry for the bother, but just thought of adding an extra point in the understanding. Looking at Paigemiller and Kurt's response, I wanted to mention what happens in the PDV when SAS reads variables from an input dataset and when SAS writes variables to the output dataset. When you use any dataset option such as (rename= drop=) in the set statement, SAS executes or in your case renames these variables before the variables are brought into the PDV whereas when you use the same in the data statement, SAS just writes the renamed variables to the output dataset at the end of the exceution. Also, using dataset option is very powerful as opposed to rename/drop statement in the datastep, it helps you filter and alter your needs at an early stage before the variables are read in the memory area PDV, thus saving a lot of execution time. I hope that helps, ... View more