A karyotype of the mitotic chromosomes of the house mouse has been prepared based upon quinacrine fluorescence patterns. All 19 pairs of autosomes and the X and Y chromosomes have been identified. Examination of the chromosomes of the following translocation stocks, T(11;?)1Ald, T(3;?)6Ca, T(2;9)138Ca, T(2;12)163H, and T(9;13)190Ca, have led to the tentative assignments of autosomal linkage groups (LG) to chromosomes as follows: LGII to chromosome number 10 (or 13), LGIII to 12 or 15, LGIX to 16, LGXI to 6, LGXII to 19 and LGXIII to 1. By definition, LGXX is on the X chromosome.