Using chromosomal in situ hybridization, multicopied DNA sequences homologous to pπ25.1 P element from 15 isofemale lines of the P strains were analyzed in a natural population of Drosophila melanogaster. The average number of copies of the P element in the 15 lines (two P, seven Q, four M' and two M strains) has determined to be 42.33. The copy number of the P element in the four strain types from the P-M system appeared more or less equally, ranged from 39.27 to 46.50 and its DNA sequences showed highly polymorphic distribution in genomic DNA per cell. The copy number on the X chromosome was slightly higher than that on individual arm of autosomes.