Rokitamycin (RKM), a 3"-O-propionyl derivative of leucomycin A5, is bactericidal against staphylococci near the minimum inhibitory concentrations. RKM bound to ribosomes before-hand is only slightly displaced by erythromycin or josamycin, or even by RKM itself. The adhesive binding of the RKM-ribosome complex might prove to be the lethal event for susceptible staphylococci.