LY146032, a new lipopeptide antibiotic, was compared with vancomycin, teicoplanin, cefamandole and ciprofloxacin, against 107 clinical isolates comprising methicillin-susceptible and methicillin-resistant Staphylococcus spp., Streptococcus faecalis and Corynebacterium spp. All staphylococci were susceptible to all agents, except that some of the methicillin-resistant strains were resistant to cefamandole. Only LY146032 and ciprofloxacin were bactericidal to Str. faecalis. Development of resistance was studied by serial transfers of ten selected strains. A stable greater than or equal to eight-fold increase of the MIC over the breakpoint was found to develop to a variable extent against all agents tested. Simultaneous development of resistance to any of the other antibiotics was registered in 11/200 tests.