Of 51 visible mutants isolated from natural or laboratory populations of Drosophila buzzatii, or X-ray induced, 42 have been assigned to chromosomes, and linkage maps have been constructed. About half of the autosomal mutants map to chromosome 2, with only two on chromosome 3 and none on chromosome 4. For the whole repleta group, chromosome 2 also exhibits much greater inversion variability than other chromosomes, which suggests variation among chromosomes in apparent mutability. The chromosomes of D. buzzatii are homologized to those of D. melanogaster and to the standard chromosomal elements of Drosophila. Sequence comparisons for six X chromosome mutant genes, whose homology is reasonably certain, in 13 Drosophila species confirm linkage group conservation but great variation among species in gene order. The linkage group conservation of single-copy genes stands in contrast to observed transpositions between elements for tandem repeat genes.