The African American Study of Kidney Disease and Hypertension (AASK) was conducted over a 7-year period at 21 clinical centers across the United States to investigate whether one of two levels of blood pressure control and/or one of three classes of antihypertensive medications was more effective at slowing the rate of renal disease in African Americans with renal insufficiency presumed secondary to hypertension. Analysis at the end of the study revealed an overall participant retention rate of 90%o (still alive and not on dialysis); defined as having had at least one [sup.125]I-iothalamate GFR, the primary data collection element, measured in the final year of the study. Adherence, ...