5-Aminolevulinic acid (ALA) and ALA ester–induced protoporphyrin IX (PPIX) fluorescence are used for photodynamic diagnosis and therapy with promising results. The aim of the present study was to investigate the detection of dysplastic lesions by fluorescence after topical application of ALA and different esterified derivatives in a model of chronic colitis in rats. In female CD rats chronic colitis was induced by oral application of 5% dextrane sulfate sodium. ALA was used at different concentrations (0.072 and 0.036 mol/L). ALA-methylester (m-ALA), ALA-hexylester (h-ALA) and ALA-benzylester (b-ALA) were used at a concentration of 0.003, 0.002 and 0.002 mol/L, respectively. Fluorescence was examined under blue light, and histological findings of fluorescent and nonfluorescent biopsy specimens were recorded. Using ALA at a concentration of 0.072 mol/L, all dysplastic lesions (8/8) showed fluorescence (sensitivity 100%). Specificity was low at 57%. Reducing the concentration to 0.036 mol/L resulted in a sensitivity of only 56% (5/9) with an increase in specificity to 76%. On using h-ALA, sensitivity was 60% (3/5) with a specificity of 51%. Using m-ALA and b-ALA, sensitivity values were 25% and 33%, and values for specificity were 62% and 63%, respectively. Despite a low number of dysplastic lesions, the results of this study indicate that ALA ester–induced PPIX fluorescence has the potential for the detection of premaligant lesions but was not superior to ALA. ALA esters were used in 18- to 36-fold lower concentrations compared with ALA.