In pharmacokinetic studies, ordinary methods of identifying or quantitatively measuring metabolites have been complicated and become difficult to handle. Here, a novel TLC-autoradioluminography (TLC-ARLG) is reported. This technique is especially suited for quantitatively measuring a minute amount, below-1 ng, of many radioactive metabolites in plasma, tissues or organs, thus eliminating cumbersome extraction procedures. The method has an extremely wide dynamic range and could offer a powerful analytical technique for studying a radioactive compound and its metabolites in a biological specimen. Autoradioluminography is a new quantitative technology developed by combining autoradiography with radioluminography. Radioluminography is a kind of radiography in which a specially designed radio-sensor plate, called an "Imaging plate (IP)," developed by Fuji Photo Film Co., Ltd., is used. The radio-sensor is made of fine crystals of BaF:Eu2+, and the technology is based on photo-luminescence phenomena.