We have reported the finding of a new mutation at the dwarf locus, named dwarf-J, gene symbol dwJ, in the C3H/HeJ inbred mouse strain. The C3H/HeJ-dwJ/dwJ mice are like DW/J-dw/dw mice in that both homozygotes are virtually devoid of GH in either pituitary glands or serum. Lifespan of dwJ/dwJ mice was not reduced. Linkage experiments designed to assign the dw gene, together with another gene weaver (wv), were successful in that both were found to be on chromosome 16. The dw locus is probably more proximally located on chromosome 16 than the wv locus.