The physical examination revealed a drowsy baby, with a body weight of 3,400 g, moderate dehy-dration, no fever, mild chest retraction, while the rest of the examination was unremarkable. The initial serum electrolytes showed the sodium, potassium, bicarbo-nate and chloride were 130, 3.4, 33.7 and 66 mEq/L. The urine electrolytes for sodium, potassium and chloride, for the same period, were 15, 7.6 and 15 mEq/L, respec-tively. After intravenous fluid re-hydration, her serum electrolytes rose to normal levels.