LY146032, a new antimicrobial agent with activity against Gram-positive cocci, was tested against methicillin-susceptible and methicillin-resistant Staphylococcus aureus, methicillin-susceptible and methicillin-resistant Staph. epidermidis, Staph. saprophyticus, and Streptococcus faecalis. MIC90s in cation-supplemented Mueller Hinton broth by the microdilution broth method were less than 1.0 mg/l for all organisms tested. Increasing or decreasing the inoculum size did not appreciably effect the MIC50 or MIC90 for any organism group nor did decreasing the incubation temperature. The addition of sodium chloride to the test system did not appreciably effect the susceptibility of methicillin-resistant Staph. aureus to LY146032. All organisms were 4 to 32 times more susceptible to LY146032 than to vancomycin. The Staph. aureus had LY146032 susceptibility patterns which were similar to those of teicoplanin and sodium fusidate. LY146032 was 4-16 times more active than teicoplanin against Staph. saprophyticus and Staph. epidermidis while teicoplanin was 8-16 times more active than LY146032 against Str. faecalis.