In the study on the definitive therapeutic effects of INHG, a new derivative of INAH, on experimental tuberculosis, hitherto no attempt has ever been made, and also in the reappraisal of toxicity of INHG, the author obtained the following results. INAH and IHMS (isonicotyl hydrazid methansulfonate) were used as the control for comparative study: 1. LD(50) of INHG, when subcutaneously injected, is 1,167 mg/kg, and when orally administered, 1,500 mg/kg; while LD(50) of IHMS, by subcutaneous injection, is 1,083 mg/kg, and by oral administration, 1,333 mg/kg. Each of these amounts to 6-8 times LD(50) of IHAH, proving the toxicity of the two to be markedly lower than INAH. 2. When 1 mg, 3 mg, or 7 mg of INHG a day is administered successively to mice with tuberculosis, tuberculous bacilli in the viscera of these mice decrease far more markedly than the same in the control, proving a striking anti-tuberculous action of this drug. 3. On coparing the effectiveness of INHG on experimental tuberculosis with that of INAH, in tuberculous bacilli culture of internal organ, even though INHG contians only 44.62 per cent of INAH, an equal volume of this drug is only slightly inferior to INAH but shows no great difference, while its weight-increasing action is stronger than INAH. In addition, the toxicity of INHG being extremely weak as already mentioned, a large dose of administration is possible, and hence clinically the application of this drug offers a promising future. 4. In comparing the effectiveness of INHG on the experimental tubereulosis with that of IHMS, no marked difference can be found between the two drugs.