In a method of monitoring a fuel cell unit, at least one pair of measured values, including a measured current value and a measured voltage value (I.sub.actual, U.sub.actual) are determined at the outputs of the fuel cell unit. The measured voltage value (U.sub.actual) is compared with a limit value (P.sub.G), which is a function of the measured current value (I.sub.actual) by way of a limit characteristic polarization curve. It is concluded that the condition of the fuel cell unit is faulty when the measured voltage value (U.sub.actual) or a function of the measured voltage value is smaller than or equal to a predefined threshold value.