A semisterile male translocation heterozygote [t(2; 14) 1Gso] that exhibited neurological symptoms and an inability to swim (diver) was found among the offspring of male mice treated with triethylenemelamine. All breeding and cytogenetic data showed a complete concordance between translocation heterozygosity and the neurological disorders. Homozygosity for the translocation seemed to be lethal at an early embryonic stage. Despite the distinctive neurologic symptoms, no anatomic or histological defects in either the ear or in the central nervous system were observed. Thus, a balanced chromosomal translocation can produce disease with an inheritance pattern that mimics a single dominant gene defect.