By applying three methods, namely, the precipitin reaction in acid medium with the antigen-antibody reaction, the measuring method of heat-noncoagulant protein in determining the serum mucoid content, and the methylene-blue reduction test using the oxdization phenomenon of sulfide ions, on the cancers occurring in the field of oto-rhino-laryngology as the follow-up study, the efficacy of these three methods has been evaluated. The following are the results of the present investigation: In the case of cancer patient before treatment the reliability of the precipitin reaction in acid medium and the measuring method of heat-noncoagulant protein shows the average rate of 80 per cent in general; and these prove to be useful as auxiliary methods for diagnosis. However, the rate of the reliability of the methylene-blue reduction test is poor and therefore its usefulness in diagnosis is low. It is worthy of attention that all these tests gave relatively high rate of positive reaction even in the subjects with diseases such as pharyngeal tuberculosis, peritonsillar abeess and tumors other than cancer. In applying these tests after the treatment, no significant difference can be recognized in the positive rate of methylene-blue reduction test as compared with that before threatment, but in the other two tests the positive rate has been markedly lowered, namely, cancer reaction tended to be negative. With respect to the course after the treatment likewise the methylene-blue reduction test does not coincide with the course of the progress, and only in the case of pharyngeal cancer the recurrence of the cancer can be observed when pseudo-positive or positive continues. The other two methods usually coincide with the course; and in the majority of recurrence cases either positive reaction precedes the recurrence or it turns positive simultaneously with recurrence. Even in the cases with satisfactory improvement, these two methods generally coincide with the progress of the disease after treatment, but there have been a few cases which were positive yet without recurrence.