Protoporphyrin IX (PpIX) is one of the photodynamically active substances that are endogenously synthesized in the metabolic pathway for heme as a precursor. Aminolevulinic acid-esters are more lipophilic than conventional 5-aminolevulinic acid (ALA) and some of them are currently being approved as new drugs for photodynamic diagnosis (PDD) and photodynamic therapy (PDT). In order to investigate the pharmacokinetics of ALA and ALA-ethyl ester (ALA-ethyl) in the atheromatous plaque and normal aortic wall of rabbit postballoon injured artery, each 60 mg kg(-1) of ALA or ALA-ethyl was injected intravenously followed by serial detection of PpIX fluorescence of harvested arteries at 0-48 h post-injection. Maximum PpIX build-up in the atheromatous plaque was seen at 2 h after injecting ALA. In contrast, it occurred at 9 h after injecting ALA-ethyl. In addition, the selective build-up of ALA in the atheromatous plaque compared to normal vessel wall was much higher (10 times) than that of ALA-ethyl. The time of maximum fluorescence intensity of PpIX was employed as drug-light-interval for subsequent PDT treatment of the atheromatous plaque with 50-150 J cm(-1) of light dose. Significant reduction in plaque was observed without damage of the medial wall at both groups, but smooth muscle cell (SMC) was still present in the media region below the PDT-treated atheromatous plaque. In conclusion, ALA may be a more effective compound for endovascular PDT treatment of the atheromatous plaque compared with ALA-ethyl based on their pharmacokinetics, but further optimization of PDT methodology remains to remove completely residual SMC in the media for preventing potential restenosis.