The findings up to 1988 indicated that one or more transport systems might be altered in essential hypertension but each system was not affected similarly, nor did all hypertensives show the same changes in each of the transport systems studied. The most consistent findings have been observed for sodium-stimulated lithium countertransport (LCT). Clinical and population-based studies have revealed that mean LCT is significantly elevated among hypertensives. In contrast, increased, decreased, and normal mean values have been reported for sodium cotransport, and increased or normal mean values for adenosine triphosphate (ATP)-dependent sodium-potassium pump activity.