In their article "New Guidelines for Potassium Replacement in Clinical Practice,"1 Jay N. Cohn et al state that "increasing potassium intake should be considered when serum potassium levels are between 3.5 and 4.0 mmol/L." Although they correctly state that a level lower than 3.6 mmol/L is not necessarily synonymous with whole-body potassium deficiency, no mention is made of the value of other findings that could lend credibility to a low value of serum potassium concentration. Such laboratory validation includes a low specific gravity of the urine, alkaline urine, metabolic alkalosis, and electrocardiographic findings of decreased T and prominent U waves.2