Preparations were obtained from the testes of six sterile males of the T(X; ?) 16H stock. 81.7% of 694 primary spermatocytes in stages from diakinesis to first metaphase contained chain quadrivalents composed of a terminal Y chromosome and three other elements that were distinguishable in length. A normal XY pair was not seen in any cell. These observations and others indicate that the stock carries an unequal reciprocal translocation between the X chromosome and one of the shortest autosomes, the break points being approximately median in both chromosomes. This suggests that the locus of tabby (Ta), which is known to be closely linked with the breakage point, lies near the middle of the X chromosome.