Allelic polymorphism of HLA-class II antigens plays a key role in the regulation of the immune response and in transplantation immunity. The allelic diversity of these antigens can now be analyzed at the DNA level after amplification by polymerase chain reaction. In this study we apply a simple technique based on the electrophoretic analysis of DNA heteroduplexes to the typing of HLA-DPB1 alleles. In order to increase its resolution, a group-specific amplification was used which subdivides the 19 HLA-DPB1 alleles in two non-overlapping families. A separate analysis was then performed within each group of alleles. This approach allowed an unequivocal one-step typing of the alleles belonging to group 1 which comprises few alleles of high frequency. Some group 2 alleles require, as a further step, the test with a restriction enzyme. The combination of more than one technique represents, in our opinion, the easiest way to solve the micropolymorphism of class II alleles. We conclude that this method, which is very simple, quick, and accurate and does not require probes, may become the method of choice for HLA-DPB1 typing.