OBJECTIVES: To identify socio-demographic, economic, medical and attitudinal factors that explain subjects' choice of test for screening for colorectal cancer (biennial faecal occult blood test versus once-only flexible sigmoidoscopy). METHODS: Data obtained from a questionnaire, administered by general practitioners and returned by approximately 2700 asymptomatic subjects. Thereafter, logistic regression modelling to explain willingness to participate in screening, whether or not a test preference is expressed, and the nature of the preference. RESULTS: An interest in undertaking screening is more probable if the subject is white, older, married and possesses a high health motivation. An intention to participate is more probable if the subjects are particularly worried about the disease, feel themselves to be particularly susceptible to it, and have already had experience of screening for colorectal and (if female) other cancers. Persons in receipt of a household income below 10,000 Pounds are less likely to express an interest in screening. Women are more likely to express a test preference and this preference is more likely to be for the faecal occult blood test. Subjects' worries and perception of risk are associated with reported experiences of cancer, stomach problems and depression. A positive attitude towards screening is positively associated with frequency of dental visits. CONCLUSIONS: Socio-demographic, economic and other factors evidently influence subjects' preferences for particular screening tests and, by implication, the likelihood of compliance with any future screening offer. The models support the view that participation in colorectal cancer screening has as much to do with a positive attitude towards health and health promotion generally as with any specific concern about the disease.