The aim of this study was to develop a rapid and safe non-radioactive DIG DNA labeling and detection for Southern blot analysis for fragile X syndrome and Duchenne muscular dystrophy (DMD). Southern blot analysis is accurate test showing expression of the (CGG)n repeat and abnormal methylation pattern of CpG island in hagile X syndrome, and good confirmative secondary test in case of deletion in DMD. But in terms of test rapidity, these conventional radioactive Southern analysis may not be feasible for rapid screening of prenatal samples and at-risk populations to determine their status and to provide genetic counseling to their families. As an alternative radioactive Southern blotting, DIG DNA labeling and detection system does not require handling of radioactive material nor require learning any new technology. The complete procedure of labeling the DNA and hybridization to detection of the first visible signal can be compbsbed witbin 7 days. In addition, hybridization solutions containing labeled DNA can be reused several times after renewed denaturation.