ABSTRACT-Pocket probing depth was correlated with the amount of salivary sialic acid in pilocarpine stimulated saliva in ODU plaque-susceptible rats (ODUS/Odu) (r=0.657, P<0.01), but not with the con tent of serum sialic acid. There was no difference in the amount of serum sialic acid content between ODUS/Odu and plaque-resistant rats. These results suggest that the amount of sialic acid in the saliva can be a useful index of the severity of periodontal disease.