It is well known that there are many substances related to the diseases at very low concentration in human body fluid. An attempt to search the new marked substances in human body fluid related the prediction of diseases has been carried out by high sensitive and simple detetecting method. In this report, the reactivities of fresh human saliva were examined by the peroxidase activity (POD) and the diminishing of the specific color (at 515 nm) of diphenylpicrylhydrazyl (DPPH)/MeOH solution used as the marker in addition of saliva. It was observed that the POD was depened on the progressing of dental caries, and that the behavior of DPPH was not similar to that of POD. Then, the color diminishing of DPPH was monotonically decresed according with the POD increase. It is expected thet this examinating method will be useful to the prodiction and the prevention of the diseases.