Stool testing based on tumour-derived markers might offer a promising approach for non-invasive colorectal cancer (CRC) screening. The aim of this study was to estimate the potential of a new test for faecal tumour M2-PK to discriminate patients with CRC from a large sample of unselected older adults. Faecal tumour M2-PK concentrations were determined in 65 CRC patients and in a population-based sample of 917 older adults (median age: 65 and 62 years, respectively). Sensitivity and specificity of the test were calculated at different cutoff values, and receiver-operating characteristic curves (ROC) were constructed to visualise the discriminatory power of the test. The median (interquartile range) faecal tumour M2-PK concentration was 8.6 U ml(-1) (2.8-18.0) among CRC patients and <2 U ml(-1) (<2-3.2; P<0.0001) in the population sample. At a cutoff value of 4 U ml(-1), sensitivity (95% confidence interval) was 85% (65-96%) for colon cancer and 56% (41-74%) for rectum cancer. Specificity (95% confidence interval) was estimated to be 79% (76-81%). Given the comparatively high sensitivity of the tumour M2-PK stool test (especially for colon cancer) and its simple analysis, the potential use of the test for early detection of CRC merits further investigation. Possibilities to enhance specificity of the test should be explored.