Jeffrey's minisatellite probe 33.15, which screens dozens of hypervariable loci throughout the genome, detects female-specific fragments in stripe-backed wrens (Campylorhynchus nuchalis). HaeIII subdivides the single large female-specific fragment observed with other enzymes into a polymorphic suite of fragments of similar total molecular weight among patterns. Sex-linked HaeIII haplotypes are perfectly transmitted from mother to daughter but not to sons. These results suggest that the female-specific HaeIII fragments represent variable subunits of a single long tandem repetitive array composed of approximately 20-bp repetitive units located outside the pairing region of the W chromosome. That sex-linked fragments do not occur in the congener Campylorhynchus griseus suggests that their entrapment and amplification on the W chromosome in C. nuchalis occurred since the divergence of the two species.Key words: minisatellites, sex chromosome, W chromosome, amplification.