Abstract: An apparatus 1 serves for treating tumors in particular. This apparatus has, for example, a sensor-actuator head 3 with at least one sensor 10 for determining the acidification of the immediate surroundings of the tumor cells. An active ingredient dispensing device for exerting chemical influence and/or electrodes for exerting physical influence through electrical and/or electromagnetic fields on the tumorous tissue area to be treated are provided on the sensor-actuator head. The sensor(s) 10 as well as the active ingredient dispensing facility and/or the treatment electrodes are connected with a control facility for controlling chemical and/or physical treatment of the tumorous tissue area as a function of measured values.