The coordinate function of two loci - pdeX and pdeY - in the genome of a transposable phage (TP) provides the phage function pde+ (good growth on bacteria with Rms163 plasmid). When these two loci in hybrid phages originate from different TP, some of the hybrid phages have Pde- phenotype. To localize pdeX and pdeY, the structure of hybrid TP genomes with Pde+ and Pde- phenotype obtained in crosses between B39ts+ and PH132 were studied using restriction and heteroduplex analysis. On the basis of data obtained, pdeX and pdeY were mapped in 2.85-6.4 and 6.4-16 kbp regions, respectively.