Linezolid was tested against 32 species of uncommonly isolated gram-positive organisms (3,251 strains) by reference MIC methods and found to be highly active (MIC50 range, 0.25 to 2 microg/ml; MIC90 range, 0.25 to 2 microg/ml). Only one isolate (viridans group streptococcus; 0.03% of tested strains) was resistant to linezolid.