The 16-membered macrolide miocamycin (MOM) has been compared with the 14-membered compounds erythromycin and roxithromycin in terms of causing post-antibiotic effects (PAE). Five strains of methicillin-resistant Staphylococcus aureus, 3 Streptococcus pyogenes, 3 S. agalactiae and 3 enterococci, of differing phenotypes of resistance to erythromycin, were tested. PAE were measured follwonig exposure of cocci to 1 x, 3 x and 10 x MICs of each antibiotic. Against the staphylococci and group A streptococci the three macrolides gave similar results, PAE of 1- h at 1 x MIC, 2-4 h at 3 x MIC and > 4 h at 10 x MIC being observed. For group B streptococci and the only erythromycin-sensitive enterococcus tested, PAE due to MOM were at least double those due to erythromycin or roxithromycin, at each concentration tested. MOM produced significant PAE for the strains that were inducibly resistant to erythromycin and roxithromycin.