In a method and apparatus for detecting tumorous cell tissue in a gastrointestinal tract, electromagnetic radiation is emitted in a locally defined manner from an endoscope onto cell tissue and, after deactivation of the radiation, the decay of the inherent fluorescence intensity of the irradiated cell tissue, excited by the electromagnetic radiation, is detected, with temporal and spectral resolution and with a known scanning rate for at least one wavelength. From the intensity measurement values obtained in this manner, the difference autocorrelation function of the intensity decay is determined, from which a fractal dimension for the irradiated cell tissue is determined. The value of the fractal dimension is used to classify the irradiated cell tissue as to a degree to which the cell tissue is tumorous.