According to recent evidence, the presence of an Arg residue at position 52 in the HLA-DQ alpha chain may confer susceptibility to Type 1 diabetes and thus be possibly used to define quantitatively the genetic risk of this disease. Arg52 and non-Arg52 DQA1 alleles cannot be typed by the conventional cytotoxicity test and they must be distinguished at the genomic level. We describe a simple procedure which discriminates the DQA1 alleles based on the differential electrophoretic migration of the DNA heteroduplexes they form with a reference DNA fragment. A major advantage of this procedure is the fact that no hybridization probe is required. Practically, this typing procedure consists of an electrophoretic run of the products of a selective PCR in polyacrylamide gel.