Virustomycin A is a macrolide antibiotic originally isolated from Streptomyces. It is active against infectious and plant pathogenic fungi, including T. vaginalis and P. oryzae (MICs = 6.25 and 12.5 µg/ml, respectively), as well as the parasite T. foetus (MIC = 25 µg/ml). It also decreases plaque formation by RNA and DNA viruses (ED = 0.0003 µg/ml for all). Virustomycin A is active against the GUTat 3.1 strain of T. brucei brucei, but not the STIB900 strain of T. brucei rhodesiense (ICs = 0.45 and 480 ng/ml, respectively), and induces cytotoxicity in human MRC-5 cells with an IC value of 80 ng/ml. It inhibits RNA, DNA, and protein synthesis in T. foetus.