Pst I RFLP, revealed with DQ alpha and DQ beta probes, was compared with Taq I RFLP using a panel of DR-homozygous cell lines and HLA-typed family members. Taq I patterns, characteristic for each DR-associated DQ alpha and beta allelic forms, were recognized in the homozygous state and then proven to segregate in the heterozygous members of informative families. The presence of both specific alpha and beta chains was found to be necessary to form the type of DQ molecule specifically recognized by two alloreactive T-cell clones. Particular alpha and beta associations also seem to be responsible for some Dw splits of the DRw6-positive cells. Taq I RFLP analysis may be more complex than the Pst I analysis, but is certainly more informative and complete, considering the type of information we were seeking by performing these types of experiments.