The mouse chromosomal location for the gene (Sp1-1) encoding the trans-acting transcription factor Sp1 has been determined. Analysis of restriction fragment length polymorphisms in recombinant inbred, congenic, and interspecific backcross mice using human and mouse cDNA probes demonstrated that Sp1-1 is a single gene closely linked to the mammary tumor virus integration site-1 (Int-1) on the distal end of chromosome 15. Sp1 is a zinc finger protein, but Sp1-1 is not closely linked to any of the other zinc finger protein genes that have been mapped in mouse. Int-1 and other markers flanking the Sp1-1 locus are part of a conserved linkage group represented on human chromosome 12q.