To investigate the electrophoretic karytype of Fusarium oxysporum, intact chromosomal DNA was separated by pulsed-field gel electrophoresis (PEGE). DNA extraction from nulcei, mycelia and protoplasts were compared with one another and with the quantity and the suitability for PFGE separation in agarose gel. As a result, the most useful extracting method for intact DNA was found to be that from protoplasts. By varying the electrophoretic conditions, 8 chromosomal DNA bounds were resolved. Using the Schizosaccharomyces pombe and Saccharomyces cerevisiae as size standards, the size of Fusarium oxysporum chromosomes was estimated to range from approximately 0.6 Mb TO 6.7 Mb, and total genome size was 26.7 Mb. The suitability of electrophoretic karyotyping as a tool for strain characterization is discussed.