Quinacrine-mustard staining and Giemsa-banding identified the large chromosome of the T1Wh translocations as No. 5; the small autosome of the translocation had previously been found to be No. 19. Others have demonstrated that translocation T163H involved autosomes 9 and 19; these findings were confirmed in our study. Meiotic studies of (T1Wh × T163H) F1 hybrids showed a chain quadrivalent at metaphase I, confirming that both translocations shared in common only chromosome 19. Metaphase II analysis of F1 hybrids demonstrated frequent nondisjunction of the T1Wh and T163H translocation chromosomes, and 12 % of 75 F2 offspring from 16 F1 crosses were trisomic for chromosome 19. Trisomics had three translocation chromosomes and a chromosome number of 38. All newborn trisomics were smaller than their normal littermates and died during the first day of life. The only specific malformation found so far has been cleft palate.