Some studies have raised the problem of an increase of bacterial resistance in acne patients. This study was carried out in France, where no previous studies about resistance to erythromycin has been performed, on 40 patients with mild to moderately severe acne. Microbiological samples were obtained by using Williamson and Kligman method. This study showed that the prevalence of bacterial resistance to erythromycin was 95% for Staphylococcus epidermidis strains and 52% for Propionibacterium acnes strains. Resistant strains were more frequent in patients with predominantly inflammatory lesions (papules and pustules). The influence of previous or current treatment with erythromycin was also studied and showed that even patients without any previous use of erythromycin had resistant strains for Propionibacterium acnes (42%). In addition the minimum inhibitory concentrations (MIC) for zinc were evaluated. All the Propionibacterium acnes strains tested were inhibited at concentrations less or equal to 512 mug/ml of zinc. However, zinc combined with erythromycin in vitro did not modify the erythromycin MIC. This first French study on bacterial resistance to erythromycin in acne patients confirms the results of studies performed in other countries.