In a comparative experimental study the glucuronic acid derivatives of isonicotinoylhydrazone (INH), isonicotinoyl-hydrazone d-glucuronic acid lactone (INHG, Gluronazid) and INH-sodium glucuronid (INHG-N-A, Gluronazid pro infusione) were shown to have the same tuberculostatic activity as INH both in vitro and in vivo. As judged by the serum inhibitory activity the serum level shows a different temporal pattern. After the administration of INHG or INHG-Na, the inhibitory activity reaches its peak later than does INH but remains in the active range essentially longer. The most substantial and, with regard to therapy, most significant difference between INHG or INHG-Na and INH lies in the varying toxicological properties. Both the oral and intravenous LD50 increase in the sequence INH, INHG and INHG-Na. The i.v. LD50 of INHG-Na exceeds the oral LD50. As compared to INH the lower toxicity permits a higher dosage of gluronazide. Thus a continuously higher serum inhibitory activity can be achieved than with a corresponding INH therapy.