The effect of sub-MICs of azithromycin, clarithromycin and roxithromycin, as compared to erythromycin, on the production of coagulase, beta-hemolysin, lecithinase and deoxyribonuclease by Staphylococcus aureus was studied. All new macrolides completely inhibited coagulase and beta-hemolysin production and partially inhibited lecithinase and deoxyribonuclease. Such inhibition is not related either to growth inhibition or to inhibition of enzyme activity. Erythromycin, on the other hand, had no effect on coagulase or beta-hemolysin production but slightly suppressed the production of lecithinase and deoxyribonuclease. This inhibitory effect might have clinical significance if it was found to occur in vivo.