Two trials of external quality assessment were performed in 2006. The first and the second trials assessed by three test categories, i.e. tumor markers, thyroid hormones and immunoproteins, such as Immunoglobulin G (IgG), IgM, IgA, Complement 3(C3) and C4. All of fourteen test items using immunoassay method were surveyed as previous years. The response rate of external quality assessment for Immunoassay Subcommittee were 98.3% and 98.1%. Ten control materials consisted of 8 home-made pooled sera and 2 commercial control sera (LyphoCheck, BioRad, USA) were used. The results are summarized as follows. 1. Laboratories participating in external quality control program of immunoassay were 259 laboratories and the response rate were 98.3% and 98.1% in 2006. 2. Chemiluminiscence immunoassay autoanalyzers were most commonly used for immunoassay testing in the clinical laboratories. 3. Still some test items show big variations of the test results of the same control material according to reagents and autoanalyzers. 4. A workshop about "Standardization of Immunoassay" was held on December 1st, 2006 in cooperation with Immunoserology Subcommittee. The quality of the participating laboratories seems to be thought being continuously improved. And, this year, many laboratories are newly participated, they were 55 clinical laboratories for the Immunoassay Subcommittee. A new surveillance system for the individual laboratory according to its performance by method and analyzer was on scheduling for special analysis and performance-basis control from next-year survey.