The Random Primer DNA Labeling Kit, Version 2 is designed for radioactive labeling for hybridization probes. Probe labeling can label DNA with [32P]-alpha-, [35S]-alpha- or [3H]-alpha-dCTP. This random primer DNA labeling kit is based on a modified method by Feinberg and Vogelstein and utilizes random oligonucleotide primers and cloned exonuclease-free E.coli DNA polymerase I, Klenow fragment. Using primers that are 9-mer and longer and exonuclease-free enzyme results in higher labeling efficiency and longer probes. This probe labeling method overcomes many of the disadvantages of conventional nick translation procedures while producing hybridization probes from very small amounts of DNA (10 to 20 ng). The Radioactive Labeling for Hybridization Probes kit can also be used to label DNA fragments that are embedded in low-melting temperature agarose gel slices.