The laser-induced fluorescence of hematoporphyrin derivative (HpD) sensitized experimental Ehrlich carcinoma on mice is investigated. The fluorescence is excited with the 364-nm argon laser line. The tumor fluorescence spectra are recorded in the red spectral region. The HpD induced fluorescence of the tumors is superimposed on the autofluorescence of tissue. The tumor fluorescence shows a maximum 4 h after i.p. application of HpD. The fluorescence intensity is reduced by strong excitation causing bleaching of the HpD absorption. The fluorescence spectrum is also changing and the generation of a fluorescent photoproduct is observed.