Two trials of external quality assessment for clinical microbiology laboratory were performed in 2001. A total of 12 specimens were distributed. Six specimens were distributed to 258 laboratories with 220 returns in Trial I and six specimens to 259 laboratories with 228 returns in Trial II. The percentages of fully correct identification of S. saprophyticus, E. faecium, E. coli, M. catarrhalis, S. agalactiae, C. krusei, S. aureus, E. coli, E. faecium, E. cloacae, C. meningosepticum, and C. albicans were 85.0%, 75.0%, 99.6%, 66.4%, 87.3%, 60.0%, 98.7%, 100%, 75.0%, 80.6%, 31.2%, and 83.6%, respectively. The acceptable percentages on disk-diffusion antibacterial susceptibility tests against oxacillin and vancomycin of S. saprophyticus (M0101) were 94.5% and 97.7%, respectively. Those against ciprofloxacin and vancomycin of E. faecium (M0102) were 96.9% and 95.3%, respectively. Those against cefotaxime and imipenem of E. coli (M0103) were 62.0% and 72.4%, respectively. In Trial II, the acceptable percentages on disk diffusion test against S. aureus (M0107) against oxacillin and vancomycin were 76.1% and 66.4%, respectively. Twenty laboratories (14.1% of total 142) on Trial II, which showed less than lower limit against vancomycin, had reported the same result on Trial II of the survey in 2000. The acceptable percentages on disk diffusion test against cefotaxime and imipenem of E. coli (M0108) were 61.5% and 67.8%, respectively. Those against vancomycin and teicoplanin of E. faecium (M0109) were 95.9% and 71.7%, respectively. The performance on the automated or E-test susceptibility tests was generally good, except in case of teicoplanin, showing the lower MIC in 37 (82.2%) of 45 participants. In conclusion, the quality assurance of the individual laboratories may not be improved only by the external quality control survey, so that the internal quality control should be performed.