Ten noninsulin dependent diabetic patients (NIDDM) without baseline hyperkalemia and with normal aldosterone levels when given 100 g of glucose orally revealed heterogeneous responses in serum potassium changes. Six diabetics had paradoxical increases in serum potassium levels averaged 0.44 mEq/L (range, 0.1 to 1.1 mEq/L) and were accompanied by increases in plasma aldosterone levels. On the contrary, four other noninsulin dependent diabetics and four nondiabetic control subjects had gradual decreases in serum potassium levels with simultaneous decreases in plasma aldosterone levels. These rises and falls in serum potassium concentrations coincided with changes in serum osmolality related mostly to the degree of increases in serum glucose following oral glucose administration. pH of venous blood didn't show any relevant and significant changes with changes of serum potassium levels following oral glucose load. This finding suggests that osmotic mechanisms with various degree of well known abnormal insulin secretion and resistance to insulin action in target tissues in NIDDM patients may account for these heterogeneous responses in serum potassium changes after glucose load, and normal aldosterone levels may not be sufficient to prevent glucose induced increases in serum potassium in NIDDM patients.