Male mice heterozygous for double translocations, involving chromosome 17, T(16, 17)43H (reciprocal) and Rb (16, 17)7 Bnr (Robertsonian), as well as mice with partial trisomy for centromeric region of chromosome 17(Ts17(16)T43H) are fertile but demonstrate a high rate of sterile matings. On the 3rd day of gestation in the progeny of males heterozygous for double translocations chromosomal aberrations were shown in 9,5% of all cleaving embryos. The number of blastomeres in embryos with partial trisomy or monosomy of chromosome 17 or 16 corresponds well to that in embryos with normal karyotype. Partial trisomy Ts17(16)T43H does not affect cleavage and early postimplantation development but may cause growth retardation during major organogenesis. Some of these embryos are probably eliminated by the end of gestation or soon after birth. Mice with translocation T43H are useful tools for studying the action of different parts of chromosome 17 at different stages of ontogenesis.