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It is shown that the frequency of spontaneous male recombination in two different lines of Drosophila melanogaster (OKI and T-007) are not subject to an interchromosomal effect. Second-chromosome male recombination in these lines was not affected by heterozygosity for the multiple third-chromosome inversions In(3LR)TM3 or In(3LR)Ubxm, which do affect recombination in females. It seems, therefore, that a large fraction of spontaneous recombination in males of D. melanogaster occurs by some mechanism other than that in females. We discuss the possibility that the mechanism is chromosome breakage and reunion, and that these breakage events may be caused by a microorganism.