RP 59500 was more potent than erythromycin, josamycin, amoxycillin and cipro- floxacin, and as potent as vancomycin, against staphylococd and enterococci. Against streptococci, the activity of RP 59500 was very similar to that of amoxy- cillin, but was superior to that of erythromycin, josamycin, vancomycin or cipro- floxacin. Compared with the other antimicrobial agents tested, RP 59500 was the most active against erythromycin-resistant Gram-positive cocci. © 1992 Oxford University Press.