The study focuses on the Laser-Induced Autofluorescence (LIAF) diagnosis technique to identify early tumor tissue. 442nm light from a Helium-Cadmium Laser is excited to investigate the spectra of the in vivo normal and tumor rat colorectal tissues. The experiment results show that the LIAF spectra of the normal and tumor colorectal tissues exhibit the significant differences. The results are potentially useful for the development of a clinical study for early colorectal cancer diagnosis.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.