A general practice-based programme was initiated in 1987 to identify individuals at high risk of developing large bowel cancer and offer them screening of faecal occult blood. In all, 5298 people from 21 general practices in the Guildford area were offered 7510 screening tests. In total, 5934 tests were completed (compliance rate 79.0 per cent) with 287 positive results (4.8 per cent). Of the patients with positive results, 44 had cancer and 38 polyps. The sensitivity of the test for cancer was 63 per cent, the specificity 96 per cent and the positive predictive value for all neoplasia 29 per cent. The detection rate of 44 cancers per 5934 people screened compares favourably with data from the Nottingham-based screening of an unselected population (0.74 versus 0.23 per cent).