Multiphoton microscopy is a powerful tool for imaging sub- cellular distribution of luminescent compounds present in living cells. We have used this tool to study the distribution and pharmacology of photosensitizers in tissue and tissue culture. Murine hepatoma tumor cells dosed with a photosensitizer were briefly photoactivated, then imaged for periods up to several hours. Using the photosensitizer Rose Bengal with green light activation, nearly immediate photolytic release of lysosomal enzymes resulted in catastrophic cell destruction within 5 - 30 minutes. The magnitude and rapidity of this response is markedly different than that observed with other photosensitizer agents, and is consistent with in vivo studies illustrating that Rose Bengal is capable of causing extremely rapid destruction of treated tumors.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.