Although erythromycin has been used in therapy for more than 25 years, until now there has been no paper summarizing the data on tissue penetration. The present review documents in detail dose- and time-related peak serum levels of erythromycin derivatives after oral administration, in addition to the erythromycin tissue levels. The erythromycin tissue levels often manifoldly exceed the corresponding MIC values of pathogens sensitive to erythromycin. However, erythromycin does not penetrate the central nervous system, or only penetrates in small, incalculable amounts. The same applies for the placental passage of erythromycin. The tissue levels confirm, with respect to the MIC values of the pathogen spectrum, clinical experience with erythromycin in the treatment of ear, nose and throat infections, respiratory tract infections and, with some limitations Chlamydia urethritis.