The behaviour of the retrotransposons copia and mdg1 was analysed in hybrids between Drosophila melanogaster and D. simulans. Females of a highly inbred line of D. melanogaster were crossed with D. simulans males from three natural populations. The insertion site profiles for the two elements were determined in F1 hybrid larvae by in situ hybridization to polytene chromosomes, and were compared with that of their parents. No somatic transposition events were detected after this genomic stress of interspecific hybridization for the two transposable elements concerned.