Macrolides have been used for decades as an important chemotherapeutic agent in the treatment of infectious diseases. In the last 10 years there has also been increasing interest in the interaction between macrolide antibiotics and the immune system. The aim of this review is to focus on the anti-inflammatory action of erythromycin and its derivatives in the treatment of chronic sinusitis and nasal polyps. Systematic clinical investigations have been few and to the author's knowledge there have been no placebo-controlled studies. However there have been, especially from Japan, a number of clinical reports stating that long-term, low-dose macrolide antibiotics are effective in treating chronic sinusitis incurable by surgery or glucocorticosteroid treatment, with an improvement in symptoms varying between 60% and 80% in different studies. In animal studies macrolides have increased mucociliary transport, reduced goblet cell secretion and accelerated apoptosis of neutrophils, all factors that may reduce the symptoms of chronic inflammation. There is also increasing evidence in vitro of the anti-inflammatory effects of macrolides. Several studies have shown macrolides to inhibit interleukin gene expression for IL-6 and IL-8 and also to inhibit the expression of intercellular adhesion molecule essential for the recruitment of inflammatory cells. There is also evidence in vitro, as well as clinical experience, showing that macrolides reduce the virulence and tissue damage caused by chronic bacterial colonization without eradicating the bacteria. The benefit of long-term, low-dose macrolide treatment seems to be that it is, in selected cases, effective when steroids fail. The exact mechanism of action is not known, but it probably involves downregulation of the local host immune response as well as a downgrading of the virulence of the colonizing bacteria. In the future, placebo-controlled studies should be performed to establish the efficacy of macrolides if this treatment is to be accepted as evidence-based medicine.