The trial of external quality assessment for inborn error of metabolism was performed in 2001. Total 5 specimens for neonatal screening tests were distributed to 68 laboratories with a response rate of 64.7% (44/68). 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 screen, homocytinuria screen and histidinemia screen. The mean, SD, CV, median and range were analyzed.