Normal phase and reversed-phase thin-layer chromatographic (NP-and RP-TLC) methods were developed for the simultaneous determination of 45 organophosphorus pesticides (OP ; 8 phosphates, 14 phosphorothioates, 15 phosphorodithioates and 8 miscellaneous OP), which were used or had been used in Japan. The pesticides were analysed by three TLC systems by using Merck Silica gel 60 F-254 plate (n-hexane-acetone 7 : 3, v/v) and Merck RP-8F₂₅₄ s and Whatman KC18F plates (methanol-water 7 : 3, v/v). The locations of the pesticides were detected by UV absorption and by colorations with palladium chloride and 4-(p-nitrobenzyl)pyridine (NBP). All of the pesticides tested could be detected with the NBP reagent, and its detection limit was less than 0.25-0.5μg of OP except 1μg of trichlorfon. The most effective discriminating powers (DP) for TLC analyses of OP were given by the combination of two TLC systems with silica gel and chemical bonded silica gels (DP=0.93 and 0.94, numbers of samples 45, and error factor 0.05). Together with our previous papers on analyses of OP by gas-liquid chromatography and directinlet and gas-chromatography-mass spectrometry (DI-and GC-MS), the most reliable procedure proposed for the examination of OP is as follows. At first, samples are applied to the TLC analyses for the screening test of OP, and then the pesticides are identified with GC-MS on column of OV-1 or QF-1 and/or DI-MS.