Citrus greening disease caused by bacterium-like organisms (BLO; greening organisms: GOs) is one of the most destructive diseases of citrus in Thailand. An efficient and reliable detection method of the pathogen is urgently needed for the control of the disease. Recently, polymerase chain reaction (PCR) method for amplifying the 16S rDNA fragment of the GOs has been developed by Jagoueix et al. (1994; Int. J. Syst. Bacteriol. 44: 379-386). We applied the method for the detection of Thai GO isolates, Nakorn-Pathum, Rangsit and Nan isolates, and succeeded in detecting the 16S rDNA fragments of the Thai isolates. Sequence analysis of the amplified 16S rDNA fragment of the Nakorn-Pathum isolate revealed that the isolate is very close to the Indian isolate of liberobacter phylogenetically. By simplifying the DNA extraction procedure, we were able to obtain DNA for PCR within 20 min, and detect the GO within 4.5 hr.