The relationship between two linkage groups, 24th and 27th, of the standard linkage maps in the silkworm, Bombyx mori, was revaluated using four visible mutants, Sel, tyw (from the 24th linkage group) Xan, and l-li (from the 27th linkage group), as markers. All cross experiments indicated that the 4 marker genes were located on the same linkage group. These data indicate that the two original linkage groups should be integrated as a revised 24th linkage group.