Heritable translocation and dominant lethal tests were conducted with random-bred Swiss albino male mice. The animals were provided drinking water containing triethylenemelamine (TEM) for 4 weeks, and were then mated for 3 successive weeks for analysis of dominant lethality and production of F1 progeny. Potential translocation carriers among F1 males were selected after two breedings and confirmed by cytogenetic analysis. Translocation heterozygotes were obtained in offspring of the TEM-treated groups, but not in the control groups. In F1 males produced from the first week of mating, the frequencies of translocations were 0, 1.78 6.2 and 10.0% for the control group and groups receiving TEM at 0.0125, 0.025 and 0.050 mg/kg/day, respectively, and in those produced from the third week of mating, the values were 0 and 2.1%, respectively, for the control group and the group receiving TEM at 0.050 mg/kg/day. F1 males from the second week of mating were not studied for the induction of heritable translocations. TEM-induced dominant lethality and heritable translocations were most prominent in the first week of mating after 4 weeks of treatment. In addition, heritable translocations appeared to be a more sensitive endpoint than dominant lethal mutations for the measurement of mutagenic effects of TEM.