The modifications of hybridization patterns were studied when Southern blots, carrying stallions DNA samples, were probed with eight synthetic tandem repeats (STRs), related by sequence variations in the basic unit. Because STRs preferentially crosshybridize with genomic VNTRs, they usually give patterns looking more like DNA fingerprints, but we found that even small modifications in the STR monomer could cause major changes in the hybridization profiles and could induce a shift of fingerprint pattern towards the detection of only one or two loci. This enables the use of STRs as direct genetic markers for linkage analysis, without cloning of the corresponding DNA fragment. Moreover, the set of STR variants can suggest consensus sequences allowing some prediction of the banding pattern.