1. This study was designed to investigate variations in erythrocyte magnesium in the presence of insulin (0.1 unit/l) in hypertensive subjects.
2. Plasma and erythrocyte magnesium levels were found to be significantly lower in hypertensive than in normotensive subjects.
3. The impaired response to insulin (0.1 units/l) of erythrocytes from hypertensive patients was not reversed by elevated extracellular Mg2+ (3.6 mmol/l).
4. Erythrocytes of hypertensive subjects showed an increased membrane microviscosity compared with normotensive subjects.
5. Lidocaine decreased erythrocyte membrane microviscosity and increased erythrocyte magnesium levels in the presence of insulin.