EDAcFN enzyme immunoassay (EIA) is a new tumour marker assay measuring the extra domain A-containing isoform of cellular fibronectin (cFN), a component mainly found in extracellular matrices. The concentration cFN was measured in plasma and serum from 468 patients with malignant and benign diseases. The concentrations of cFN were higher in plasma than in serum. Using receiver operating characteristic (ROC) curve analysis, determination from plasma was superior to serum at specificity levels higher than 78% and was chosen for further analysis. The highest frequencies of elevated cFN values were seen in patients with hepato-pancreato-biliary malignancies (50-67%). In pancreatic and bile duct cancers, cFN provided little further information to that obtained by CA 19-9. The greatest advantage over CA 19-9 and CEA was seen in patients with local colorectal cancer and in hepatocellular carcinomas. Four out of nine patients with Dukes' stage B colorectal cancer had an elevated cFn level, but only one had an abnormal CEA level. In hepatocellular carcinomas, cFN was also compared with alpha-fetoprotein. The sensitivity of cFN (72%) was superior to that of AFP (61%), and concomitant use of cFN and AFP raised the sensitivity to 83%. The highest frequencies of elevated values in patients with benign diseases were observed in those with severe liver disease (32%) and biliary (17%) and pancreatic (24%) diseases. A combination of cFN and CA 19-9 showed the highest overall sensitivity of 47%, compared with 31% for cFN and 33% for CA 19-9. The corresponding specificities were 76% for cFN +/- CA 19-9, 85% for cFN and 83% for CA 19-9. The accuracy of a combination of cFN and CA 19-9 or CEA (60% respectively) was higher than that of cFN (55%), CA 19-9 (55%) or CEA (45%) alone. In conclusion, the results of the new cFN test are encouraging and further studies on larger patient materials have been started.