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George L. Petrikkos, Associate Professor, 1st Department of Propedeutic Medicine, Athens University School of Medicine, Laiko, General Hospital, GR-115 27 Athens (Greece) From the previous very interesting presentations the following main points can be outlined: Dr. Höffken noted that the isolation of the agent responsible for respiratory tract infections (RTIs) is desirable, but it is difficult to differentiate between pathogen and commensals. The decision to treat is based usually on epidemiological, clinical and radiological assessments. The difference in the etiological spectrum of community and hospital-acquired RTIs, the underlying disease and immunosuppression are crucial in the decision for treatment. Penicillins or macrolides are the drugs of choice, while the new oral cephalosporins exhibit excellent activity against many bacterial pathogens of typically community-acquired RTIs caused by resistant strains oïHaemo-philus influenzae and other ß-lactamase-producing gramnegative bacteria. Dr. Cullmann discussed the importance of ß-lactamase stability in treating RTI, and noted that nowadays 70 to 90% of Moraxella catarrhalis are ß-lactamase-producing (bla+) isolates. The enzymes BRO-1 and BRO-2 which are transposon mediated explain their rapid spread. Bla+ H. influenzae isolates make up 6% of the total in Northern Europe, up to 55% in Southern Europe and in many African countries more than 80%. Resistance is mainly due to the prevalence of the most widespread transposon-me-diated TEM-1 ß-lactamase. Recently, new extended spectrum enzymes (TEM-3 to TEM-21) inactivating even the oxyiminocephalosporins have arisen by mutation from TEM-1 or TEM-2 enzymes. The compounds least affected by these enzymes are ceftibuten and cefetamet. Professor König explained the role of the immune system in recovery from infection. The efficacy of nonspecific as well as specific host defence mechanisms is obligatory to counterbalance microbial infection. He described the process of inflammation by the release of mediators, the regulation by cytokines of endothelial-granulocyte interaction and migration of granulocytes to the focus of inflammation, the triggering of the humoral or cell-mediated immune response, antibody formation and allergic reactions. Microorganisms can activate or deactivate the host response thus facilitating opportunistic microbial growth. Dr. Scheffer presented data on the effect of several oral cephalosporins on inflammatory host reactions. Cefaclor, but not the oral cephalosporins cefetamet, Ro 40-6890 or cefpodoxime increased histamine release from human basophils. A significant increase in phagocytosis in the presence of various cephalosporins was demonstrated and the bactericidal activity of human granulocytes for several bacterial strains was also enhanced. Cefetamet, cefaclor, Ro 40-6890 and cefpodoxime increased the chemiluminescence response of human neutrophils