The highly polymorphic variable number of tandem repeat (VNTR) loci in the human genome are informative markers for the genetic characterization of individuals in the paternity test and forensic science as well as for the study of human disease. In this study, VNTR loci D1S80 and D2S123 have been amplified by PCR and the amplified length polymorphic alleles were detected with a discontinuous vertical PAGE system and silver staining. For explicit DNA typing, PCR optimization, in which amplification efficiencies are similar over a wide range of allele sizes, non-specific amplifications are minimal, and new longer alleles have high amplification efficiency, has been performed by changing the PCR reaction buffer composition and thermal cycling conditions. It turned out that adding an appropriate amount of Tween 20 and NP40 to the PCR reaction buffer and raising the annealing temperature to $68^{circ}C$ in thermal cycling made it possible for optimal VNTR loci amplification. A modified PAGE system for VNTR separation was established. Under these conditions, new longer alleles in the 01580 locus were discovered and 025123 pattern changes in colorectal tumors were observed. These technical tips are valuable for detecting various amplified fragment length polymorphisms.