The color reaction with a 0.5% alcoholic solution of aromatic amine and the irradiation of ultraviolet light resulted in the feasibility of detecting a few μg of chlorinated pesticides on the thin-layer chromatogram. Sensitivities by the various chromogenic agents used in this method are given in Table 2. Obtained Rf values of the chlorinated pesticides and photocopy of their chromatogram are given in Table 3 and Figure 1 Stahl has indicated that more precise Rf values could be acquired by considering the correlation between each Rf value of chemical compounds and that of a standard dye. Then we used a 0.5% benzene solution of anthracene in substitute for the standard dye he described. According to our experiments, the spots of both DDT and anthracene always show the same Rf values so that we are able to presumably identify not only DDT but other pesticides in comparison with a spot of anthracene, even if in the absence of standard pesticides.