A human DNA probe specific for the superoxide dismutase gene was used to identify the corresponding mouse gene. Under the chosen hybridizing conditions, the probe detected DNA fragments most likely carrying the mouse Sod-2 gene. Mapping studies revealed that the Sod-2 gene resides in the proximal inversion of the t complex on mouse chromosome 17. All complete t haplotypes tested showed restriction fragment length polymorphism which is distinct from that found in all wild-type chromosomes tested. The Sod-2 locus maps in the same region as some of the loci that influence segregation of t chromosomes in male gametes. The possibility that the Sod-2 locus is related to some of the t-complex distorter or responder loci is discussed. The data indicate that the human homolog of the mouse t complex has split into two regions, the distal region remaining on the p arm of human chromosome 6, while the proximal region has been transposed to the telomeric region of this chromosome's q arm.