Abstract The shaker mutants Hk1 and Sh5affect the nervous system and reduce lifespan, perhaps through activity-related metabolic rate. Three hundred y w Hk1, y w Sh5, and y w mosaics were generated by an unstable ring-X, scored for external male and female tissues, and kept singly to determine the lifespan of each. Because the mosaics did not resolve themselves into distinct long- and short-lived categories, a computer curve-fitting method was developed to transform and combine the appropriate non-mosaic male (short-lived) and female control curves of percent dying per day, into an approximation of the curves observed for mosaics with a given cuticular landmark male on both, one, or neither side. The resulting estimates of long- and short-lived mosaics of each type were used to calculate the distance between each landmark and the developmental focus for Hk1 and Sh5 life-shortening. In both cases the mutant focus was in the ventral anterior part of the thorax, perhaps in the anterior thoracic ganglion; the focus was submissive for Hk1 and domineering for Sh5. At the same time,there was a second focus, independent of the mutant effect, associated with early mosaic death. In both shaker and control mosaics this early death focus mapped laterally in the region of the wing, and is probably the result of incompatible juxtapositions of male tissue in that region, and female tissue anteriorly. The curve-fitting method may be useful for analyzing other quantitative and multi-focus characters.