A long-term clinical study is underway to evaluate the merit of occult stool blood testing in the earlier detection of colorectal cancers; 48,000 participants have been enrolled. Thus far, 873 patients with occult stool blood have been examined, and 77 gastrointestinal cancers have been found in 74 patients. Although data from the control group are not yet available for comparison, most of the cancers found appear to be relatively early in their development. Conventional barium-enema examinations were noted to have “missed” one third of the colon cancers and two-thirds of the colon polyps which were found on colonoscopy. Preliminary results of the study appear encouraging. Definitive analysis will await the availability of additional pertinent data.