The invention relates to an application substance reservoir (9) for a toothbrush, said reservoir having a data carrier (13) and being filled with toothpaste or any other substance to be applied, and to an electric toothbrush (1). Preferably, the actual level of the application substance reservoir (9) and/or the type of substance to be applied is stored in the data carrier (13) of the application substance reservoir (9). The electric toothbrush (1) has a data receiver for reading data stored in the data carrier (13), a data transmitter for writing on the data carrier (13) and a control device which indicates in response to the read data for example the level in the application substance reservoir (9) of the respectively used substance to be applied. Data can also be stored in the data carrier (13) for adapting the toothbrush operation to the respectively used substance to applied, said data causing the control device to operate the toothbrush accordingly.