The molecular and phenotypic analysis of several previously described P element-transformed lines of Drosophila simulans was extended in order to determine whether they had the potential to produce a syndrome of P-M hybrid dysgenesis analogous to the one in Drosophila melanogaster. The transformed line with the highest number of P elements at the beginning of the analysis, DsPπ-5C, developed strong P activity potential and P element regulation, properties characteristic of D. melanogaster P strains. The subsequent analysis of sublines derived from 34 single pair matings of DsPπ-5C revealed that they were heterogeneous with respect to both their P element complements and P activity potentials, but similar with respect to their regulatory capabilities. The subline with the highest P activity, DsPπ-5C-27, was subsequently used as a reference P strain in the genetic analysis of the D. simulans transformants. In these experiments, the reciprocal cross effect was observed with respect to both gonadal sterility and male recombination. As in D. melanogaster, the induction of gonadal sterility in D. simulans was shown to be temperature-dependent. Molecular analysis of DsPπ-5C-27 revealed that it has approximately 30 P elements per genome, at least some of which are defective. The number of potentially complete P elements in its genome is similar to the number in the D. melanogaster P strain, Harwich-77. Overall our analysis indicates that P-transformed lines of D. simulans are capable of expressing the major features of P-M hybrid dysgenesis previously demonstrated in D. melanogaster and that P elements appear to behave in a similar way in the two sibling species.