Immunogenic analyses were carried out for the rhizobial isolates collected from South Indian soils using the extracellular polysaccharide as the antigen. They are immunogenic eventhough their immunogenic nature was not established unequivocally in the previous studies. There was wide variation in their monosaccharide composition which could not be correlated with serological reactions.IR studies of these exopolysaccharides reveal that there are two major functional groups, amide and carboxyl in most of the isolates. The immunodiffusion analysis revealed that there are four distinct bands common to all the isolates. The antisera of the isolates D2, D9, V2, V3, Sa1 and P1 showed an additional hazy line.