The locus of the structural gene encoding tyrosine hydroxylase, Th, the rate limiting enzyme for catecholamine biosynthesis, was mapped to the distal end of mouse Chromosome (Chr) 7. A DNA probe of genomic origin of rat tyrosine hydroxylase was used to detect restriction fragment length variants among 8 inbred mouse strains. The strain distribution pattern of Th allelic variants in 3 sets of recombinant inbred mouse strains was determined. Comparison of the strain distribution patterns of Th alleles with those of previously typed loci suggested Th was located on Chr 7. The Chr 7 assignment for Th was confirmed by analyzing 108 mice produced from an (NZB X SM)F1 X NZB backcross. Moreover, the Th locus was positioned distally on Chr 7. Mouse Chr 7 and human Chr 11p (the location of the human tyrosine hydroxylase gene) are known to share several homologous loci. With the addition of Th, the homology between the distal 2/3 of mouse Chr 7 and human Chr 11p appears extensive.