The typing of HLA class II genes using molecular biology techniques has brought undoubtedly new insights in the analysis of their polymorphism. Particularly interesting is the dot-blot analysis of enzymatically-amplified genomic DNA hybridized with sequence-specific oligonucleotides. In order to use this technique of typing on a routine basis, we established a non-radioactive detection method of enzymatically-amplified genomic DNA dot-blots. We could clearly demonstrate that, using biotin-labelled specific oligonucleotides, it was possible to specifically discriminate between DQB1 first domain DNA sequences displaying three, two or even only one base-pair difference at a given codon position. The very satisfactory sensitivity level reached by this non-radioactive detection method could safely allow its use for clinical applications of HLA typing at the DNA level.