Randomized controlled trials (RCT) of colorectal cancer (CRC) screening using guaiac faecal occult blood tests (gFOBT) have consistently demonstrated significant reductions in disease-specific mortality,1 and this evidence has led to the introduction of screening programmes using tests for the presence of faecal haemoglobin (f-Hb) in many countries. This evidence concerns the gene GSTM1 and colorectal carcinoma.