We offered a questionnaire to 52 physicians in order to study the appreciation of the fecal occult blood test as an example of a diagnostic procedure. We asked for an indication of the over-all appreciation of the test, and for an estimation of the probabilities of colorectal cancer before the test and with a positive or a negative test result — each of them for three situations with different a priori probabilities. The answers demonstrated that the estimated value of the test, representing the personal experience of the physicians is very low (predictive factor between 0.61 and 0.78). About half of the physicians' estimations showed no improvement of probability by using Haemoccult. This contrasts with the expressed very positive general opinion about Haemoccult testing, including its use in symptomatic patients. This result underlines the necessity of careful evaluation of diagnostic tests.