We have developed a new immunochemical test for fecal lactoferrin (LF) utilizing an enzyme-linked immunosorbent assay (ELISA). The ELISA had a sensitivity of about 10 micrograms/L of lactoferrin and the measurable range was 10.0-1000.0 micrograms/L (1.0-100.0 micrograms LF/g feces). The stability of lactoferrin in feces was greater than that of myeloperoxidase and leucocyte elastase. The fecal concentration of lactoferrin (mean +/- SD) in 35 normal subjects was 0.75 +/- 0.83 microgram/g feces, whereas that in 24 patients with colon cancer was 74.4 +/- 88.3 micrograms/g feces. The fecal lactoferrin concentration of 38 patient with active ulcerative colitis was 307.4 +/- 233.9 micrograms/g feces, and that in 36 patients with active Crohn's disease was 191.7 +/- 231.1 micrograms/g feces. The ELISA for human fecal lactoferrin might be useful in the diagnosis of colon disease.