For question 1, I think this is the complete list.  The DATA step retains (a) any variable mentioned in a RETAIN statement, (b) the first variable in a SUM statement, and (c) any variable that comes from a SAS data set (regardless of whether the SAS data set is being read with a SET, MERGE, or UPDATE statement). For question 2, yes the variable is retained.  Your programming statements may overwrite that retained value, however. To illustrate, you might try creating some variations on these programs: data test1;    put 'Before:  ' x=;    input dummy;    retain x;    x=_n_;    put 'After:  ' x=; datalines; 8 9 ; data _null_;    put 'Before:  ' x=;    set test1;    x=_n_ + 10;    put 'After:  ' x=; run; ... View more