Plasmid-like DNA (plDNA) was found in 10 out of 61 field isolates of Fusarium oxysporum. These 10 isolates were distributed among 6 formae speciales. Electron microscopic analysis revealed that all these plDNAs were linear molecules. The sizes of plDNAs found were varied from 1.9 to 8.0kb. The sequence homology among four 1.9kb plDNAs, pFOA, pFOL, pFOC and pFOR found in four different F. oxysporum formae speciales was examined by Southern blot analysis, using nick-translated plDNAs as probes. Considerable sequence homology was observed among pFOA, pFOL and pFOC DNA, but pFOR had no homology with three other 1.9kb plasmid DNAs. pFOM and pFOB DNAs of the sizes of 8.0 and 2.2kb, respectively, had no sequence homology with four plDNAs of 1.9kb.