The ability of agrobacteria [Agrobacterium tumefaciens, A. radiobacter] to adhere to host sites [pinto bean] may be determined by either chromosomal or plasmid genes which affect LPS (lipopolysaccharide) structure. Because the structural features of LPS essential for adherence are unknown and the degree of variation consistent with adherence is unknown, the effect of the plasmid and chromosomal determinants may or may not be identical, although they could have equal relevance to the infection process. It seems probable that most virulent agrobacteria have both chromosomal and plasmid genes which can determine adherence, since both the K14 and B6S3 virulence plasmids confer site binding ability on non-site binding recipient strains and since 4 ''naturally'' virulent strains (C58, ACH5, B91 and 181) when cured of their virulence plasmid retain site binding activity, as does avirulent plasmid-free strain ATCC4718. Determination of the structure of LPS which is essential for adherence in different strains of agrobacteria and the discovery of means to cure additional strains of their plasmids will resolve these relationships.