The dissonance mutant of courtship song was induced by chemical mutagenesis. This X-chromosomal mutation causes the D. melanogaster male's acoustical output, resulting from his wing vibrations directed at a female, to include very long and loud tone "pulses." Yet, a given train of pulses starts out as normal, with the signals in all but the shortest singing bouts eventually becoming polycyclic and high-amplitude. The aberrant songs caused by diss (map position, 1-52; cytological interval, 14C1-2 to 14C4-5) were quantitatively compared to those produced by mutant cacophony males, whose pulses are much more uniformly polycyclic (due to a mutation mapping elsewhere on the X chromosome). Males or females expressing diss are normal in several "general" behaviors. Yet diss males not only sing abnormally, but they also exhibit longer-than-normal mating latencies in their courtship of females. These decrements seem to be associated, at least in part, with visually aberrant behavior of diss flies--measured with regard to male courtship per se, and also in tests of more general visual responses. Such defects were found when testing diss males or females, and the genetic etiology of the visual impairments were provisionally mapped to the same locus to which the song abnormality has been localized. Neurogenetic connections between the control of courtship singing behavior and visual system functions are discussed with respect to the new song mutation (diss) and the older one (cac)--which also turned out to be genetically related to a mutation that causes abnormalities of light-induced behavior and physiology.