To examine the role of DNA loci within the human leukocyte antigen (HLA) region and insulin-dependent diabetes mellitus (IDDM), we studied fine mapping of HSP70-2 gene. Polymerase chain reaction (PCR)-based genotyping was then developed and applied to type HSP70-2 in 59 patients with IDDM and 83 unrelated controls recruited from the inhabitants of northern Taiwan. Southern blot analysis revealed a diallelic PstI polymorphism of the HSP 70-2 gene, i.e., 9.6- and 8.5-kb alleles. The polymorphic site was mapped in the intragenic PstI sequences (nucleotides 1051-1056) of the HSP70-2 gene. PCR-based restriction fragment length polymorphism studies revealed that the frequency of the 8.5-kb allele was increased in IDDM (56.8%, vs. 40.4% in controls; p < 0.009), with a relative risk of 1.93 (95% confidence interval = 1.20-3.11). The genotypic frequencies of 9.6/9.6, 9.6/8.5, and 8.5/8.5 were 17.0, 52.5, and 30.5% for IDDM were different from those of controls (36.1, 47.0, and 16.9%, respectively; the homozygous 9.6/ 9.6 genotype was significantly decreased in the IDDM group, p < 0.02). In conclusion, we provide a simple, rapid, and nonradioactive method for HSP70-2 genotyping. Our data confirmed that the 8.5-kb allele of HSP70-2 was associated with IDDM susceptibility in the Taiwanese population.