An enhanced chemiluminescence reaction has been incorporated into an enzyme immunoassay (EIA) for human basic fibroblast growth factor (hbFGF). We developed a new luminol derivative, designated L-012 and a new enhancer, 4-(4-hydroxyphenyl)thiazole. Using these compounds, the detection limit of hbFGF was improved to 0.1 pg/assay, which was 10-20 and 2 times better than the o-phenylenediamine colorimetric and luminol chemiluminescence assays, respectively. The average concentration of bFGF in sera from 25 normal volunteers was 5.9 pg/ml. On the other hand, serum bFGF levels were elevated in renal, lung and brain tumor patients. The data presented here indicate that the serum bFGF level could be a useful diagnostic marker for these tumors. Furthermore, these new compounds could easily be applied to any other EIA that uses horse radish peroxidase to improve sensitivity.