Surveys of the public's and general practitioners' knowledge of colorectal cancer, and their views on screening for the disease, were conducted. There were gaps in knowledge in both groups. Most general practitioners were not in favour of screening by means of faecal occult blood testing (haemoccult). Nearly 18,000 men and women aged between 40 and 70 years, registered with 41 general practitioners, took part in a randomised trial of compliance with screening for colorectal cancer using haemoccult. There was a significant (p < 0.001) difference in compliance between the three methods of invitation which were studied. Compliance was highest (57%) in the group who were offered the test by their general practitioner during a routine consultation, compared with sending a letter and test (38%) or sending a letter with an appointment to attend the surgery (49%). Giving half each group an educational booklet about bowel diseases and screening had no effect on compliance. Compliance was significantly (p < 0.001) higher in the older (55-70) age group, in women, in households in which two or more people were offered screening, and in one of the two study areas. A sample of those who had been offered the haemoccult test, and half of the one per cent of positive cases, were followed up. The majority of respondents, who had received a letter of invitation from their general practitioner, had not been upset or offended. The majority of the positive cases interviewed were pleased they had done the test, but some criticisms were expressed of their hospital management.