Greening disease of citrus is caused by a phloem-restricted, bacterium-like organism (BLO). DNA was purified from phloem tissue of periwinkle plants infected with an Indian strain of the greening BLO, restricted with HindIII endonuclease, and cloned in the replicative form of bacteriophage M13mp18. By differential hybridizations involving DNA from healthy and infected periwinkle plants, we have selected three recombinant phages containing BLO DNA. The BLO DNA inserts (In-2.6, In-1.9, and In-0.6) have been purified from the viral replicative forms and used as probes. Southern and dot hybridizations have shown that In-2.6 and In-1.9 recognized all asian strains tested (strains from India, Thailand, the Philippines, Indonesia, China, and Taiwan), but not a South African strain. In-0.6 reacted only with the indian BLO strain.