[Early detection of gastrointestinal tumors (author's transl)].

"Early cancers" of stomach and colon have a favourable prognosis, but mass screenings for these tumors with endoscopic or radiographic methods are ineffective and expensive. The simple nonspecific test for occult blood as a suitable method for early detection of stomach and colorectal cancer in high-risk patients seems to be more useful. Some suggestions are given to detect and to control risk groups.