Mutations at the period (per) locus in Drosophila melanogaster alter rhythmic components of the male courtship song. We have examined the mating speed of females homozygous for mutant per alleles when presented with artificial mutant songs. Mutant females retain a preference for wild-type over mutant songs, thus male song and female preference are probably under separate genetic control. In contrast, per-mutant females from an established laboratory stock which had been maintained for nearly two decades appear to have an enhanced response to the corresponding mutant song in that they no longer discriminate against mutant song. These results are discussed in terms of the "genetic coupling" and "coevolution" theories of complementarity between male and female components of communication system.