Two new dimeric cyclohexapeptides, chloptosins B and C, were discovered from the culture broth of Embleya sp. MM621-AF10 together with the known compounds chloptosin and L-156,602. The structures of the new chloptosins were determined by spectroscopic studies and advanced Marfey's methods. The stereo structure of the constituent isoleucine was determined by C3 Marfey's analysis. Chloptosins demonstrated potent antimicrobial activity against Gram-positive bacteria including drug-resistant strains of methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci with MICs of 0.5-2 µg ml-1. The antimicrobial activities of chloptosins were enhanced by addition of co-producing compound L-156,602, as shown by checkerboard analysis.