Abstract: The method for diagnosing microprogrammed computers consists of locating malfunctioning computer circuits with the aid of basic control data from which individual basic control words are selected under the control of diagnostic control data, and activating those basic microorders contained in the selected basic control words which provide for execution of a predetermined diagnostic procedure. A device for effecting the above method comprises two groups of NAND gates, as well as two flip-flops. The first inputs of the NAND gates of each group are connected to respective outputs of a diagnostic control data storage and the second inputs are connected to the output of the flip-flop whose input is coupled to the output of a diagnostic unit. The outputs of the NAND gates of the first group are connected to the inputs of the control unit of a basic control data storage. The outputs of the NAND gates of the second group are connected via NOR gates to the activate inputs of respective decoders.