Fluorescence spectroscopic detection using 5-amino levulinic acid (ALA) may provide an effective, noninvasive approach for early detection of oral cancer. In the present study, the use of ALA-induced fluorescence ratio (red/orange) to differentiate between normal and gingivitis-affected gingiva is investigated. Five dogs with varying degrees of gingivitis are studied. Based on previous studies, a dose of 25 mg/kg of ALA is administered intravenously to the dogs. Autofluorescence and ALA-induced fluorescence from three sites: normal gingiva, pigmented gingiva, and gingivitis, are detected with a fiber optic probe coupled to an optical multichannel analyzer. Four dogs show higher and earlier ALA-induced fluorescence from the gingivitis site as compared to the unpigmented gingiva. In two dogs, ALA-induced fluorescence peaks are seen 15 min after ALA administration. Statistical analysis using mean separation procedures reveal differences in the fluorescence from the various sites in each dog. Using a fluorescence (ratio) cutoff of 1.5, the sensitivity and specificity are found to be 92 and 80%, respectively, 1 h after administration of ALA. The indications from this study—that the characteristic protoporphyrin IX (PpIX) fluorescence is seen earlier and in higher magnitude in more vascular areas of the oral cavity—has implications for oral cancer diagnosis.