A controlled study was made in Burgundy (France) to assess the acceptability and efficiency of colorectal cancer screening using the Hemoccult test. A total of 91,000 people aged 45 to 74 years were included. The first screening campaign was made from January to July 1988 or 1989, and rescreening occurred from January to July 1990. During the first 4 months of the campaign, the General Practitioners (GPs) offered the test to their patients. It was then mailed to all subjects who had not completed it with a recall letter, if necessary, one month later. The overall compliance rate was 54.0% in the first campaign and 55.5% in the second campaign. A total of 63.7% subjects had completed at least one screening test over the two screening campaigns. Compliance was lower among men than women; compliance rate was also lower in the youngest and oldest age group than in the intermediate age groups. During the second screening campaign, the participation rate was 83.6% among participants in the first screening campaign and 20.9% among non-participants. Compliance during the medical offer phase was higher (81.4% during the first campaign, 82.9% during the second campaign) than during the postal offer phase (respectively, 33.8% and 28.5%). It was easier for GPs to propose the test when they had to offer it than when they had to prescribe it. These results suggest that a satisfactory participation rate can be obtained in France if GPs are actively involved in the screening programme. The final objective is to find a 25% difference in 5-year mortality by large bowel cancer between the screened and the test population.