New applications of low-C 0 t DNA are reported as probes for genetic identification and genome characterization. These fast and intermediately reannealing fractions have sometimes either been discarded in genomic library construction to enhance the probability of finding single copy genes, or they are used as resources for identifying individual repetitive sequences. In addition, they are used as blockers to enhance hybridization signals. C 0 t-1 DNA serves as a probe for DNA fingerprinting of human yeast artificial chromosomes. We have isolated low-C 0 t DNA from bacteria, fungus, plant, mussel, chicken, rat and fish from the sheared genomic DNA of the respective species. Low-C 0 t DNA is labeled to generate DNA fingerprints and for in situ hybridization. Individual specific DNA fingerprint profiles are observed and species-specific DNA fragments can be identified in bacteria, fungus, plants (Ginseng and Amaranthus) and mussel. When low-C 0 t DNA probes from rat, chicken and fish were employed, only smear profiles and no distinct DNA banding patterns were evident. In these species, individual clones can be used as a probe for DNA fingerprinting containing repetitive sequences after subcloning. The advantage of this approach is to quickly develop a useful probe for DNA fingerprinting for genetic identification and analysis without sequencing knowledge a priori. This represents an innovative approach to the use of these repetitive components of the genome.