Participation rates in colorectal cancer (CRC) screening programmes using faecal occult blood tests (FOBTs) are low. Nonparticipation is commonly attributed to psychosocial factors, but some medical conditions also prevent screening. These barriers might be partially overcome if a blood test for CRC screening was available. This study determined whether people who had always declined screening by FOBT would participate if offered a blood test. An audit of registrants within a personalized CRC screening programme was undertaken to determine the reasons for regular nonparticipation in FOBT. Consistent nonparticipants (n=240) were randomly selected and invited for CRC screening with a blood test. Demographic characteristics and the reasons for prior FOBT nonparticipation were collected by means of a questionnaire. Nonparticipation in the screening programme could be classified as either behavioural (8.6%), with consistent noncompliance, or due to medical contraindications (8.5%), which included chronic rectal bleeding, being deemed unsuitable by a health professional, and needing personal assistance. Blood test uptake was 25%, with participation in the medical contraindications group greater than that in the behavioural group (43 vs. 12%, P<0.001). Reported behavioural reasons for nonparticipation in faecal immunochemical test included procrastination and dislike of the test, but these were not associated with blood test uptake (P>0.05). There is a subgroup of the community who have medical reasons for nonparticipation in CRC screening with FOBT but will participate if offered a blood test. The option of a blood test does not, however, improve uptake in those who admit to behavioural reasons for noncompliance with screening.