In turbocharged engines, there is the problem that, in particular under load, the ambient pressure (AMP) cannot be determined directly from the measurement values of a charge-pressure sensor (8). In order to avoid the installation of a further pressure sensor which is suitable for the detection of the ambient pressure (AMP), it is proposed that, during a negative load step of the internal combustion engine in which a switch takes place from supercharged engine operation into non-supercharged engine operation, the charge-pressure sensor (8) measures the transient profile of the charge pressure (PUT). A value for the ambient pressure (AMP) is determined from the transient profile of the charge pressure (PUT). Through the pressure value for the present ambient pressure (AMP), it is possible to optimize the engine operation for example when travelling up a slope.