Polymorphism and linkage of mouse soluble aconitase (Aco-1) and galactose-1-phosphate uridyl transferase (Galt) are reported. Three alleles at each locus were recognized on the basis of differences in electrophoretic mobility. Linkage crosses involving Aco-1, brown (b), major urinary protein (Mup-1), and the Rb(4.6)2Bnr Robertsonian translocation (Rb2) showed that Aco-1 is located on the proximal portion of chromosome 4 between (Mup-1) and the centromere. Because Aco-1 and Galt are located on the short arm of the human 9, linkage of mouse Aco-1 and Galt was thought to be likely. Linkage crosses involving Rb2, Galt, Aco-1, Mup-1, and b confirmed this expectation and established the order of loci as: centromere--Galt--Aco-1--Mup-1--b. The conserved linkage of Aco-1 and Galt in mouse and man probably represents an ancient linkage not yet disrupted by chromosomal rearrangement, rather than a linkage preserved by natural selection.