I conducted clinical studies on application of the speech aid for the purpose of improving nasopharyngeal function in those patients who still had speech disturbance due to nasopharyngeal insufficiency even after palatal repair. For the treatment of speech disturbance accompanying cleft palate, it is necessary to perform palatal repair to restore nasopharyngeal function to its normal level as early as possible and also to give systematic speech therapy. However, we encounter not infrequently cases with residual speech difficulty due to nasopharyngeal insufficiency even after such palatal repair. For this reason, I carried out clinical studies on 64 cases by applying the speech aid in order to improve their nasopharyngeal function and giving speech therapy. As a result I have drawn the conclusions as follows. 1. For the improvement of nasopharyngeal function and normalization of speech, the speech aid seemed to be indicated for those those patients with expiration loss rate of over 2.1 at the time of blowing with Taguchi's manometer. 2. When the speech aid applied was classified into four types according to the morphology and function of its palatomaxillar section, there were 36 cases (56.2% ) for whom the palatomaxillar section was used for the sole purpose of supporting the pharyngeal section, but in the cases of bilateral and unilateral cleft lip and palate patients there were 63.4% of them for whom speech aid was used for restore the tooth defect and hard palate perforation. 3. Among 29 cases whose cephalometric x-ray films were taken at the time of pronouncing the vowel "a", the cases showing Passavant's bar amounted to 66.5% , where the upper margin of Passavant's bar was in contact with the posterior inferior edge of the pharyngeal section, which coincided with the produced under the direct view of mirror, but in those cases not revealing Passavant's bar there could be observed no definite position-relationship. 4. With growth of the jaw the speech aid applied in 3-5 year old children had to be reconstructed in the majority of cases, and the duration of time from the first speech aid insertion to the first reconstruction set ranged 19 months to 23 months. 5. The speech aid proved to bo effective on nasopharyngeal function in 85.9% of the cases applied, bringing up the respiration loss to O point at the blowing time, which in the majority of them had been attained within 4 months after the application of speech aid. Especially marked was such an effect in those cases whose palato-pharyngeal sphincter function before the application was good, some even showing an immediate effect. 6. As to the speech improvement after the application of speech aid, there were 41.7% , of the cases recovering to normal speech level (degree one), and 22.9% of them who could carry on normal speech (degree two), revealing the application to be most effective in the age range of 3 to 6 years old. 7. As for the relation of speech improvement to repiration loss rate, in the cases whose respiration loss rate recovered to O after the application of speech aid there were 48.8% whose speech improvement reached degree one and 26.8% of them degree two, but in all those whose respiration loss rate did not recover to O, there was recognized a residual cleft palate speech (degree 3) that existed prior to the application of speech aid. 8. After the application of speech aid it required a speech therapy suitable to each individual in a narrow sence for a certain length of time, and most of the patients over one year old but under two years had to be given speech therapy. 9. There were some cases of auditory disturbance with slight hearing difficulty that seemed to affect the speech recovery, hence cases with auditory disturbance require oto-rhinologic therapy. 10. It had been shown that the application of speech aid inhibits speech recovery effect in the cases of markedly low intelligence so that the speech aid was preferably indicated for those with intelligence of over (IQ=80). 11. Factors contributing to the interference of speech recovery were mental disturbance, auditory disturbance and poor family environments, and it is essential to discover the most suitable methods to eradicate these factors or to develop speech therapy most suitable for individual cases. 12. In the cases of unoperated submucous cleft palate, speech aid proved to be effective, for those cases of relatively young age with a good palato-pharyngeal sphineter function. 13. We tried adjustments of speech such as reduction of pharyngeal section by scraping on 20 cases whose speech had recovered to normal, and we found 5 cases whose speech aid could be removed, 8 cases whose pharyngeal section had shrunken, and 7 cases whose one could not be reduced in size. 14. The cases removed of speech aid were lower aged-children and had the good function of the palato-pharyngeal sphincter and the sufficient length of soft palate, and by the age of 7 years both the anterior to posterior diameter and the left-to-right diameter of the pharyngeal section had shrunken to 5 or 6mm and they showed the shrinkage rate of less than 1/2 in comparing that before and after scraping. Macroscopic examinations of these cases revealed the enhancement of the palato-pharyngeal sphincter function, especially marked was the functional improvement of the pharyngeal lateral wall in the majority of cases. In addition, the cephalometric x-ray films showed an improved movement of soft palate, a marked Passavant's bar, and the shortening of the minimum distance between the soft palate and Passavant's bar. 15. From these findings it seemed that in order to achieve the most ideal result with speech aid we should plant to restore speech level to its normal at first with speech aid, then to scrape the pharyngeal section gradually while observing patient's speech manner, and finally to try to remove the speech aid as soon as feasible.