A total of 209 lines derived from a Korean population (Cheonan) of Drosophila melanogaster were tested with respect to the P-M system of hybrid dysgenesis. The P factor activity appeared to be nearly inactive or null. In the tests for cytotype and P activity, about 47% of tested lines were characterized as M cytotype (M' strains) and the remaining lines (53%) as P cytotype (Q strains). Based on in situ hybridization with a full-sized 2.9kb P element probe, the Q and M' strains were found to have 35.6±10.3 and 34.5±9.7 copies of P elements in the genome, respectively. Among these P element in the genome, Q and M' strains were found to have 2.4±0.5 and 2.1±1.6 copies of complete P element, showing on hybridization with a 0.67 kb PstI probe derived from internal region of a full-sized P element. On the basis of results for the genomic distribution of P elements and strain types, Korean populations of D. melanogaster appeared to have a mixed population structure similar to that of the coastal areas of China and the continental areas of Central Asia.