Correlation of the testicular determinant factor sequence zinc finger Y with varying gonadal phenotypes in a series of 13 subjects with gonadal dysgenesis due to Y aneuploidy. Deoxyribonucleic acid samples from a series of 13 subjects with 45,X/46,X,altered Y, and varying gonadal phenotypes (streak-streak, n = 9; streak-testis, n = 2; testis-testis, n = 2) were analyzed for the presence of the candidate testicular determinant factor sequence zinc finger Y. The Y-specific probes Y97 mapped to Y centromere, pDP105 A,B mapped to Yp and distal Yq11, respectively, hybridized with the deoxyribonucleic acid from all the 13 study subjects. The same deoxyribonucleic acid samples were analyzed for the presence of the zinc finger Y sequence. Eleven of the 13 subjects were positive for the zinc finger Y sequence. Four zinc finger Y-positive subjects had unilateral (n = 2) or bilateral (n = 2) testicular differentiation. Among the nine subjects with bilateral streak gonads, seven showed the presence of this sequence. The lack of testicular differentiation in the presence of quantitatively normal or almost normal zinc finger Y bands could not be explained by mosaicism alone. Mutations not detectable by analysis with the method of Southern with pDP1007, may occur in the testicular determinant factor gene vitiating testicular development. 