Recombination between two mouse t–haplotypes, tw12tf and tLub-1, was investigated by screening the tailless progeny of the cross ♀ tw12tf/tLub-1 + × ♂Ttf/+tf for the segregation of tufted phenotype, tw12 and tLub-1 lethal factors, and metacentric chromosome (since tLub-l haplotype is associated with a Robertsonian fusion involving chromosomes 4 and 17). The results give a 17% estimate of the recombination frequency between centromere and tf, with tLub-l lethal factor mapping about two-thirds of the distance from centromere to tf and the tw12 lethal factor behaving as if closely linked to tf. This further extends the findings of Silver & Artzt (1981) and of Artzt, McCormick & Bennett (1982), and shows that two t–haplotypes with quite independent laboratory histories recombine at a normal level, supporting the notion that all t–haplotypes basically share the same structure.