Taitomycin is a new antibiotic isolated from the mycelium of S. afghaniensis^1,2,3). It is highly active against gram-positive bacteria, pathogenic anaerobic bacteria, gram-negative cocci, leptospira and rickettsiae, but not against gram-negative bacilli, acid-fast bacteria, fungi, yeasts, trichomonads, toxoplasma and Ehrlich mouse ascitic tumor. It is the purpose of this paper to describe the therapeutic effect of taitomycin on experimental psittacosis in chick embryo and mouse.