A new hereditary tail anomaly (gene symbol Tal) in rats was found in the course of teratological studies with trypan blue. The characteristic feature of the tail anomaly was a short and kinked tail. The genetic analysis indicated that the tail anomaly was caused by an autosomal dominant gene and the homozygotes were lethal in the prenatal stage. The first sign of degeneration in the homozygous embryo appeared in the late egg cylinder stage. The phenotype of this mutant is similar to that of T-locus mutants in mice.