In the systematic study of the effects of various drugs administered for a long period of time on the liver function in 54 cases of lung tuberculosis presenting the background factor common to all, the author arrived at the following conclusions, 1. Along with the effect of the chemotherapy a marked improvement can be observed in the serum protein picture and also a striking increase in the albumin content and a significant rise in A/G can be recognized. Since the improvement in the serum protein picture is especially marked in mild cases irrespective of which drug is administered, it is assumed that this is the result of lung tuberculosis beining affected by the chemotherapy rather than by the specificity of the drug itself. 2. SM never interferes with the liver function and it tends to bring the function back to the normal level. 3. PAS will normalize the liver function along with the improvement of the lung symptoms, but it occasionally induces a transient and mild disturbance. 4. INH likewise normalizes the liver function along with the therapeutic effect, but it may induce a transient and mild distnrbance in a relatively rare instance. 5. In the combination therapy of two or three of SM, PAS, and INH the change in the liver function does not differ from that in the single treatment. In some instances the combination therapy of PAS and INH brings about a transient and mild disturbance, but generally with the improvement of tuberculous symptoms the liver function is normalized. 6. In the combination therapy of PZA plus INH in some instances the liver function returns to the normalcy along with its excellent therapeutic effect, but on the other hand, in a prolonged treatment there is a tendency of inducing the disturbance in the liver function. However, in such a treatment no critical disturbance such as of jaundice can be recognizid, and there is no impediment in the continuous treatment. 7. It is clinically worthy of note that occasionally the disturbance of the liver function occurs during the treatment with the use of PZA, PAS, and INH as can be seen from the above, and therefore, it is significantly important to observe carefully the change that may occur in the liver function in the course of chemotherapy.