I don't know why you would not use &W as the parameter in your macro call, since its value is unchanged for your entire data step. But you may be looking for the RESOLVE function, which provides a means to delay resolution of a macro call until data step execution - i..e it's a means of having the data in a given record influence what the macro returns.  As in: %macro t(arg);   %if &arg=2 %then 2;   %else 3; %mend t; data have;   do a=1 to 2;output; end; run; data _null_;   set have;   b=a*resolve(cats('%t(',a,')'));   put a= b=; run; But this will probably generate a significant performance hit, which you can test by multiplying data set HAVE to, say 100,000 observations.  Then run the above data _null_ step (take out the put statement), and compare its speed to this data _null_ step: data _null_;   set have;    if a=1 then b=a*%t(1);    else b=a*%t(2); run; ... View more