10'-Desmethoxystreptonigrin is an antibiotic originally isolated from Streptomyces and a derivative of the antibiotic streptonigrin. It is active against a variety of bacteria, including S. aureus, S. faecalis, E. coli, K. pneumoniae, and P. vulgaris (MICs = 0.4, 1.6, 3.1, 3.1 and 0.4 µg/ml, respectively). 10'-Desmethoxystreptonigrin is cytotoxic to HCT116 colon and A2780 ovarian cancer cells (IC50s = 0.004 and 0.001 µg/ml, respectively), as well as HCT116 cells resistant to etoposide and teniposide and cisplatin-resistant A2780 cells (IC50s = 0.003, 0.001, and 0.01 µg/ml, respectively). 10'-Desmethoxystreptonigrin is also an inhibitor of p21ras farnesylation (IC50 = 21 nM).