A new rex or curly coat mutant in the Norway rat is reported. The vibrissae are bent, the coat is shorter than normal and has a harsh texture. The condition is due to a dominant gene designated rex (symbol Re). The coat of the homozygote (ReRe) is more severely affected than the heterozygote (Re+) and displays a transient baldness at about five weeks of age. Careful comparison suggests that Re is probably distinct from the four rexoid mutants previously described in the Norway rat.