MACROLIDES, one of the oldest antibiotic classes, are widely used in out-patient clinics and hospitals. The major improvement in developing newer derivatives concerns pharmacokinetic properties. Increased half-lives, persisting concentrations in tissues, interstitial fluids and macrophages confer upon newer macrolides significant advantages as compared with the parent compound erythromycin. ROXITHROMYCIN, a newer macrolide has a high peak serum concentration, providing very high levels both in the interstitial fluid and intracellularly. PHARMACODYNAMIC APPROACHES are still limited with macrolides, however the very high inhibitory quotient established for tissue concentrations and interstitial fluid suggests the potential clinical efficacy of these drugs.