The invention relates to a method for operating a diesel engine in which an air ratio (.lamda.) of the fuel which is to be burnt and of the combustion air supplied is set by a control unit (14) according to predetermined values. When a value (15) which is predetermined as a switching criterion is recorded, the control unit (14) switches to a special operating mode for regeneration of a catalytic converter (22) and sets the fuel/air ratio according to predetermined values for this operating mode.To achieve more effective regeneration of the catalytic converter, according to the invention it is provided that at least one afterinjection, which is separated in time from a main injection, of fuel which is also to be burnt takes place in the special operating mode.