The majority of known plant resistance genes encode proteins with conserved nucleotidebinding sites and leucine-rich repeats (NBS-LRR). Degenerate primers based on conserved NBS-LRR motifs were used to amplify analogues of resistance genes fromthe dicot sugar beet. Along with a cDNA library screen, the PCR screen identified 27 genomic and 12 expressed NBS-LRR RGAs (nlRGAs) sugar beet clones. The clones were classified into three subfamilies based on nucleotide sequence identity. Sequence analyses suggested that point mutations, such as nucleotide substitutions and nsertion/deletions, are probably the primary source of diversity of sugar beet nlRGAs. A phylogenetic analysis revealed an ancestral relationship among sugar beet nlRGAs and resistance genes fromvarious angiospermspecies. One group appeared to share the same common ancestor as Prf, Rx, RPP8, and Mi, whereas the second group originated fromthe ancestral gene from which 12C1, Xa1, and Cre3 arose. The predicted protein products of the nlRGAs isolated in this study are all members of the non-TIR-type resistance gene subfamily and share strong sequence and structural similarities with non-TIR-type resistance proteins. No representatives of the TIR-type RGAs were detected either by PCR amplification using TIR typespecific primers or by in silico screening of more than 16,000 sugar beet ESTs. These findings suggest that TIR type of RGAs is absent fromthe sugar beet genome. The possible evolutionary loss of TIR type RGAs in the sugar beet is discussed.