A high speed full automatic ELISA system for measurement of insulin-like growth factor-I (IGF-I) was established by using magnetic particle-linked monoclonal antibody and enzyme-labeled monoclonal antibody. A standard curve was obtained, and the effect of dilution on the assay system was investigated. An IGF-I spike recovery test of human serum samples and a study of the correlation with a radioimmunoassay system were performed, and good results were obtained from all studies. The assay range was 0.5-50 ng/ml, and the time required for the full automatic measurement was 15 minutes. This assay system will play a central role in the clinical approach to IGF-I.