Photodynamic diagnosis (PDD) is a form of cancer detection based on the administration of an exogenous photoactivated compound that accumulates in malignant tissues, followed by adequate photo irradiation. 5-aminolevulinic acid (ALA) is a prodrug of photosensitizer protoporphyrin IX (PpIX). The efficacy and optimal timing of ALA-based PDD was evaluated in mouse NR-Si squamous cell carcinoma of the tongue. Fluorescence was induced with a pulsed Nd: YAG laser after administration of ALA (200ga kg^-1intraperitoneally, or 400mgkg^-1orally). ALA-induced PpIX fluorescence intensities of about 635nm in the tumor and adjacent normal tissues were measured. Maximum fluorescence intensities in the tumors were recorded 1 hour after intraperitoneal administration and 2 hours after oral administration of ALA. The PpIX fluorescence (i. p. and p. o. routes of ALA administration) had returned to background levels within 24 hours. PDD following administration of ALA may provide an effective approach for detection of oral cancer.

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