Sp3 belongs to a large family of transcription factors that bind GC/T box elements. We have previously demonstrated the deficient expression of Sp3 in peripheral blood mononuclear cells (PBMC) from most patients with multiple sclerosis (MS). In the current study, the Sp3 gene was assigned to chromosome 7 by using somatic cell hybrid mapping and analysis of a chromosome 7-specific cosmid library. The position of Sp3 was refined to 7p14-p15.2 by fluorescence in situ hybridization (FISH). Southern blot and polymerase chain reaction analysis of genomic DNA failed to demonstrate a detectable difference between MS and control PBMC.