A new probe for the determination of fructose and glucose has been assembled using a platinum electrode and three enzymes co-immobilized on its surface: fructose dehydrogenase, glucose dehydrogenase and diaphorase. The mechanism of this probe is very simple: when the probe is immersed in a solution containing fructose and glucose and an electrochemical mediator, the current signal is due to the fructose. Then, by adding NAD(P)+a current response due to the glucose present in solution is obtained.