A method and a system for the non-invasive temperature determination on biological tissue, particularly at the fundus of the eye, treated by a treatment radiation, particularly laser radiation, wherein, during the respective irradiation time, at essentially identical time intervals, additional radiation pulses of a shorter pulse duration and a lower energy are aimed at the treated biological tissue, the resulting tissue expansions and/or contractions being detected by a pressure measurement or optical measurement and, from the measuring signals, the absolute temperature values are determined and optionally the treatment radiation is controlled as a function thereof.