To the Editor.
—In their analysis of renal function data from the Multiple Risk Factor Intervention Trial (MRFIT), Walker et al1 report that among all treated hypertensive patients and among those with controlled diastolic blood pressure (DBP, <95 mm Hg), renal function improved in nonblack men, but declined in black men. We believe that these important conclusions should be treated cautiously. First, as the authors state, the study is limited by the inclusion of only a small number of blacks, and second, the study fails to account adequately for the possibility that major socioeconomic differences might confound what appear to be racial differences.Of the 5524 hypertensive men studied in MRFIT, only 463 were black. The importance of this limitation can be seen, for example, in the analysis of the influence of blood pressure control on renal function among blacks. Surprisingly, blacks whose blood pressure was controlled (DBP, <95