Two trials of external quality assessment for inborn error of metabolism was performed in 2000. Total 11 specimens for neonatal screening tests were distributed to 68 laboratories with a response rate of 77.9%(53/68) in trial I, with a response rate of 72.1%(49/68) in trial II. All the control materials were sent as filter paper forms. Each laboratory replied the test results as the screening items they were testing routinely at the reception of the specimen among PKU screening, neonatal TSH, neonatal T4(total/free), galactosemia, homocytinuria and histidinemia screen. The mean, SD, CV, median and range were analyzed.