The aim of this study was to investigate the effect of Cha-em Thai (Albizia myriophylla) mouthwash on the mutans streptococci (MS) and immunoglobulin A (IgA) level in saliva. Sixty-seven schoolchildren, age 6-12 years, with MS more than 1x10(5) cfu per milliliter of saliva were entered in this study. They were divided into two balanced groups according to their baseline MS counts (> or = 10(5) cfu/ml). Each group was randomly assigned to use either the Cha-em Thai mouthwash or the placebo mouthwash. After twice daily rinses with their mouthwash for 2 weeks, stimulated saliva were collected and analysed. The MS counts and IgA levels for the two groups were compared. Those rinsing with Cha-em Thai mouthwash showed a significant reduction in MS counts (p<0.05), but the IgA levels were not different. Those rinsing with the placebo mouthwash showed no statistically significant differences in the MS counts or the IgA levels (p>0.05). The results indicate that twice daily use of Cha-em Thai mouthwash can reduce the levels of MS in saliva.