This study confirms the presence of a novel variable number of tandem repeats polymorphism, designated as HumDN1, in intron 4 of the human deoxyribonuclease I (DNase I) gene. Genotyping was performed without difficulty by PCR-amplification and separation by agarose gel electrophoresis in 423 Japanese, originating from four geographically diverse areas in Japan, and 89 Germans. The HumDN1 allele variability was due to different numbers of 56-bp repeat sequences, and five different alleles were distinguished with apparent size between 364 and 588 bp. Although there was a general uniformity for the polymorphism in the Japanese population, significant differences in genotype distribution were found between the Japanese and German populations. Furthermore, linkage disequilibrium between the HumDN1 and DNase I protein polymorphisms was revealed.