A total of 314 isolates of Streptococcus pneumoniae collected by 10 different laboratories were tested for their susceptibility by using a microdilution technique following NCCLS recommendations. The following antibiotics were included: penicillin, ampicillin, amoxicillin, amoxicillin/clavulanate, cefaclor, cefuroxime, cefotaxime, imipenem, ciprofloxacin, gemifloxacin, levofloxacin, erythromycin, clarithromycin, azithromycin, miocamycin, clindamycin and tetracycline. The insusceptibility rate (IR) to penicillin was 21.0% [10.8% intermediate (> or = 0.12-1 microgram/mL) and 10.2% high-level (> or = 2 micrograms/mL)], to cefotaxime 7.3% [3.5% intermediate (> or = 1 microgram/mL) and 3.8% high-level (> or = 2 micrograms/mL)], to imipenem 3.8% [3.8% intermediate (> or = 0.25-0.5 microgram/mL) and 0% high-level (> or = 1 microgram/mL)], to ciprofloxacin 11.2% [8.3% intermediate (2 micrograms/mL) and 3.9% high-level (> or = 4 micrograms/mL)], to erythromycin 30.3% [3.5% intermediate (0.5 microgram/mL) and 26.8% high-level (> or = 1 microgram/mL)] and to tetracycline 38.5% [0.9% intermediate (4 micrograms/mL) and 37.6% high-level (> or = 8 micrograms/mL)]. No decreased susceptibility was found for gemifloxacin (> or = 0.5 microgram/mL). This compound was the most active with MIC50, MIC90 and an IR of 0.015 microgram/mL, 0.03 microgram/mL and 0% respectively, followed by amoxicillin/clavulanate, amoxicillin and imipenem (MIC50, MIC90 and IR: 0.015 microgram/mL, 1 microgram/mL, 1.6%/0.015 microgram/mL, 1 microgram/mL, 1.9%/0.008 microgram/mL, 0.12 microgram/mL, 3.8% respectively). Compared to the 1999 surveillance, penicillin and tetracycline-insusceptibility increased with 4.9% and 15.6% respectively, while cefotaxime, erythromycin and ciprofloxacin insusceptibility decreased with 5.4%, 5.8% and 4.4% respectively. MICs of all beta-lactams rose with those of penicillin for penicillin-insusceptible isolates. Imipenem, cefotaxime, amoxicillin and amoxicillin/clavulanate were generally 4, 2, 1 and 1 doubling dilutions respectively more potent than penicillin on these isolates while ampicillin, cefuroxime and cefactor were generally 1, 2 and 4 dilutions respectively [table: see text] less potent. Most penicillin-insusceptible isolates remained fully susceptible to amoxicillin/clavulanate (92.4%), amoxicillin (90.9%) and imipenem (81.8%). Erythromycin-tetracycline insusceptibility was the most common resistance phenotype (14.3%). Three- and four-fold resistance was found in 12.4% and 1.6% respectively of the isolates. Most penicillin-insusceptible isolates were of capsular types 14 (22.7%), 23 (21.2%), 6 (18.2%), 9 (13.6%) and 19 (12.1%).