An instrument for coagulation and dissection of biological tissue including a tool with coagulation electrodes and at least one cutting electrode. The electrodes are actuated via an operating circuit including an evaluation circuit, to which an external apparatus delivers an evaluation signal with first and second half-waves having opposite polarities. During at least one first half-wave, the evaluation circuit checks whether a first switch or a second switch are actuated on the instrument. Depending on the evaluation result, a triggering signal is transmitted to a switching unit. Depending on the triggering signal, the switching unit is switched into a first or second switching state. In the second switching state, no voltage suitable for dissection and no current suitable for dissection, respectively, is applied to the cutting electrode. In the first switching state, a voltage suitable for dissection or a current suitable for dissection is applied to the cutting electrode.
