Fiber optic probes used to deliver and collect light for biomedical fluorescence spectroscopy applications have varied widely in design. Critical design parameters include fiber diameter, tissue fiber-tip spacing, and illumination- collection fiber separation distance. While device design has been shown to influence spectral distributions, previous studies have not thoroughly addressed how probe geometry affects the spatial origin of detected fluorescence or how probe design might be customized for specific tissue sites or applications. We have developed a Monte Carlo model of laser-induced fluorescence and investigated the effect of design parameters on light propagation using gastrointestinal tissue optical properties. The distribution of emission locations for detected fluorescence were calculated. Initial results indicated that average fluorescence emission depth and total signal intensity are highly dependent on fiber size and tissue-fiber spacing. The implications of these results for optimization of probes used in the detection of neoplasia are discussed.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.