The locus for the mitochondrial malic enzyme (ME2) seems to be closely linked to the gene coding for the A subunit of coagulation factor XIII (F13A). From 18 informative families with 54 children a maximum lod score of 4.33 was obtained at a recombination fraction of 0.10. Since the assignment of F13A to the short arm of chromosome 6 was recently confirmed, the locus for ME2 can be added to this linkage group. The map order seems to be: GLO1-HLA-F13A-ME2.