A multicentric study of the incidence of pneumococcal serotypes was recently carried out in five different geographical areas in Italy. Two hundred and sixty-seven strains were typed using the quellung reaction with monospecific antisera, but only 28 of these were isolated directly from the site of infection. The most frequent serotypes were 19, 6, 3, 9, 4, 1 and 18 without remarkable differences regarding the area, age of patients and site of isolation. It was found that 60.3% of the serotypes isolated from all sources and 67.8% of those isolated from the sites of infection are contained in the currently used antipneumococcal vaccine. Antibiotic resistance was found versus aminoglycosides (34.9%), tetracycline (28.3%), chloramphenicol (5.2%) and penicillin (3.3%). Cefoxitin appeared to be the antibiotic to which the pneumococci were most susceptible. Only two types, 19 and 16, resulted resistant to all the antibiotics.