DuP 105 and DuP 721 are two members of the oxazolidinones, a new class of synthetic antimicrobial agents with activity against gram-positive bacteria. In vitro tests compared the two new drugs with five other antimicrobial agents against 216 gram-positive isolates representing 4 genera and 10 species. DuP 721 MICs for 50% of the strains tested (MIC50s) ranged from 2.0 to 8.0 micrograms/ml, DuP 105 MIC50S ranged from 4.0 to 16 micrograms/ml, and vancomycin MIC50S ranged from 0.25 to 1.0 microgram/ml. Methicillin-resistant and -susceptible staphylococci were susceptible to ciprofloxacin, vancomycin, and DuP 721.