The results of the clinical examination of 288 diphtheria carriers, 300 diphtheria patients, and 100 diphtheria convalescents ready for discharge are given. It is shown that the proportion of abnormal conditions in the nose and throat of the carriers (94.1 per cent.) is higher than in the diphtheria patient group (73 per cent.), and considerably higher than in the recovered convalescent cases (52 per cent.). This is particularly noticeable when the proportion of cases with nasal abnormalities is considered in the three groups, namely, in carriers 72.2 per cent.; in diphtheria patients 42.6 per cent.; while in negative convalescent cases the figure is only 7 per cent. Further, the departures from normal in the recovered convalescents are generally enlarged but healthy looking tonsils which do not appear to interfere with the natural elimination of diphtheria bacilli during convalescence.The greatest proportion of carriers is in the age group 1 to 5 years, and owing to the small size and anatomical complexities of the nasal passages, the pathological conditions tend to persist and make examination and treatment difficult. The figures indicate that the presence of pathological conditions in the nose and throat of diphtheria patients is conducive to the establishment of the carrier state.It has been shown during the investigation that the presence of diphtheria bacilli in carriers is intermittent, and that there may be failure to isolate the organisms over long periods of time although the patient may still be infective.It is emphasized that even three negative culture results are not sufficient to establish that a carrier is completely free from infection.