The point made by Drs Hering and Carlson is well taken. In my attempt to be brief, I did not go into all the ramifications and implications of the serum creatinine level as a measure of renal function. The nomogram that they supply is useful, especially when the serum creatinine level is at the upper range of normal. However, the regimens described in my article would not have to be modified until the serum creatinine level is definitely above the normal range, even in elderly patients who would have lower creatinine clearances than young patients for any given level of serum creatinine. I do not believe that Drs Hering and Carlson are suggesting that clearances should be done for all elderly hypertensive patients.