Seventy-nine second lethal chromosomes and ninety-nine third lethal chromosomes were established from male Drosophila melanogaster collected from Daejon, Korea. These chromosomes were isolated by using balancer strains with pure M type. After 31-38 generations, these chromosome lines and the additional one hundred twenty isofemale lines, prepared from the population, were analyzed for gonadal dysgenesis (GD). The distribution of P elements on larval polytene chromosomes was also examined by in situ hybridization method using biotin-labeled pπ25.1 DNA probes. The results showed: (1) the isofemale lines consisted of Q (55%) and M’ (45%) strains, (2) the percentages of GD sterility in F1 females from crosses between females of each lethal lines and π2males were polymorphic, particularly, the rates of cytotype conversion to P were 2.7%, 19.4% in the second and the third lethal lines, (3) the copy numbers of P element per genome were 33.3, 27.6, 25.0 in the isofemale lines, the second, and the third lethal lines, respectively, (4) the redistribution of P elements from the second lethal chromosomes to X and third chromosomes, or from the third lethal chromosomes to X and second chromosomes were also observed after 31-38 generations. The results indicated that the Daejon population of D. melanogaster may contain autonomous P elements that caused the cytotype conversion and interchromosomal transposition of P elements.