Various methods, with different strengths and weaknesses, are currently used to define polymorphism of the bovine major histocompatibility complex (MHC) class II genes. A more complete characterization of bovine lymphocyte antigen (BoLA) haplotypes can be achieved by combining several of these methods. In this study BoLA class II polymorphism was characterized using three typing methods: serology, restriction fragment length polymorphism (RFLP), and isoelectric focusing (IEF). Twenty six Holstein-Friesian and 15 Angus cattle that carried an array of serologically defined BoLA haplotypes were selected for the study. The panel included 12 BoLA complex homozygotes. The three class II typing methods recognized polymorphism associated with the same or very tightly linked genes in the DQ-DR class II subregion. In total 25 BoLA-A locus (class I)--DQ-DR subregion (class II) haplotypes were defined. Three of the serological class II specificities, Dx1, Dx3, and Dx4, were associated with more than one RFLP defined DQ-DR haplotype. The other 4 class II specificities behaved as private specificities. One BoLA haplotype was found in both Holstein and Angus cattle. Two other BoLA haplotypes defined here have previously been described in other breeds. This suggests that these haplotypes exist in strong linkage disequilibrium.