Drosophila melanogaster males carrying a ring-X-chromosome were X-rayed and crossed to virgin females of 7 stocks, which had their second and third chromosomes systematically substituted. In the same experiment dominant lethals, sex-chromosome losses, and reciprocal translocations were recorded. Maternal effects on mutation fixation were observable as differences in the mutation frequencies observed with the different types of females. With the set of substitution stocks studied it was found that the maternal genotype strongly influences the frequencies of chromosome losses. The influences on classical chromosome-breakage phenomena, such as dominant lethals and translocations, however, are weak. The differences in the chromosome-loss frequencies may result either from different time intervals between insemination and the beginning of chromosome replication, and/or the efficiency of a repair system. One or more strong genetic factors responsible for such modifications could be located on the third chromosome. On the second chromosome, at best only weak factors are present.