Method of regulating an internal combustion engine in order to reach presettable nitrogen oxide emission values of the internal combustion engine, wherein the internal combustion engine is supplied at least some of the time with a first fuel and at least some of the time with a second fuel, the quantity of the first fuel supplied to the internal combustion engine per unit of time being controlled according to a preset control actual value or kept constant and the quantity of the second fuel supplied to the internal combustion engine per unit of time to reach a presettable nitrogen oxide emission value being regulated according to at least one recorded engine parameter.