An apparatus for the treatment of biological, in particular living tissue comprising a treatment laser device 1 for generating a pulsed treatment radiation directed on to a target tissue, in an embodiment additionally including a measurement laser device 2, 3 for generating a pulsed measurement radiation directed on to the target tissue of lower energy and shorter pulse duration than the treatment radiation, a detector device 4 for measuring pressure transients induced by the measurement radiation and a control device 6 for controlling the treatment radiation in dependence on the pressure transients evaluated in respect of a tissue change, wherein a regulating or control algorithm for controlling the treatment radiation is formed from the pressure transients.