A family of new antibiotics, named rifamycins have been recently discovered by Sensi, et al.^1～4) Rifamycin SV, a derivative of rifamycin B, is highly active against Gram-positive bacteria and tubercle bacilli in in vitro experiments⁵⁾. Its toxicity in animals is extremely low⁶⁾.

Timbal and Brega⁷⁾ stated that rifamycin SV delayed the mortality of mice infected with tubercle bacilli. Monaldi, Curci and Nitti⁸⁾ made basic studies on the antituberculous action of this drug and reported that this drug was effective against experimental tuberculosis in guinea pigs.

The purpose of the present study is to deal with the antituberculous action of this drug and to present some findings on the nature of action.