A viable t-haplotype, t38, has been shown to distort linkage relations in the T−tf region of mouse chromosome 17. Separate experiments were done with two different interstitial markers, Low and qk, which map respectively about 5 and 4 centimorgans (cM) from the locus of T in female T + tf/ + (Low or qk)+ heterozygotes. In females that carried t38, however (i.e. t38+ + / + Low tf or t38+ + / + qk tf), there was virtually no recombination between t38 and either interstitial marker, although the t38−tf distance was normal. These observations suggest that t38 suppresses recombination in the lefthand part of that region and strongly enhances it further to the right.