In a method for operating an SCR catalytic converter provided for the reduction of NOx in exhaust gases of an internal combustion engine, which SCR catalytic converter is operated with a reagent which can be stored in the SCR catalytic converter such that there is a certain reagent fill level in the SCR catalytic converter, wherein the actual NOx concentration downstream of the SCR catalytic converter is monitored on the basis of the signal of a sensor, which is arranged downstream of the SCR catalytic converter and which is sensitive at least with respect to NOx, in comparison with a calculated NOx concentration downstream of the SCR catalytic converter, it is provided according to the invention that, in the case of a comparison result which represents a conversion deficit as a difference between the measured actual NOx concentration and the previous calculated reagent fill level in the SCR catalytic converter is corrected to a new calculated reagent fill level, whereby an immediate dosing of reagent takes place.