One thousand, eight hundred and fifty-six Streptococcus pneumoniae strains, collected in 1992 and 1993 from 15 centres in Western Europe and USA were tested for susceptibility to 16 antibiotics. The overall resistance to penicillin was 23% (range 6-54%), with the highest prevalences in Madrid, Barcelona, Toulouse and Cleveland. Seven centres reported low-level penicillin resistance only. Amoxycillin was more active than ceftriaxone against strains with intermediate resistance to penicillin, and at least four-fold more active than cefuroxime; cefaclor and cefixime had poor activity. Against penicillin-resistant strains, ceftriaxone was slightly more active than amoxycillin, cefuroxime exhibited borderline activity and cefixime and cefaclor were inactive. Ten strains fully susceptible to penicillin had MICs of ceftriaxone > or = 0.1 mg/L; this may represent a first step towards the development of cephalosporin resistance. With the exception of fluoroquinolones, resistance to non-beta-lactam antibiotics (chloramphenicol, doxycycline, co-trimoxazole, erythromycin, clarithromycin and azithromycin) was considerably higher in penicillin-resistant strains compared with penicillin-susceptible isolates. Erythromycin-resistant isolates were also resistant to the other macrolides tested.