['Control of pre-analytical variables is essential for successful application of biological markers, including bone resorption markers, in clinical trials and routine use. The effect of storage temperature on stability of bone resorption markers have not been subject of systematically investigation, and therefore the present study was set out to determine the stability of C-telopeptides of type I collagen (CTX) in serum and plasma samples stored frozen for 3 years.', 'The serum and plasma levels of CTX were determined in samples aliquoted and stored frozen for up to 3 years.', 'No significant decrease could be detected in neither serum nor plasma samples after 3 years of storage at -20, -80 or -150 degrees C. However, at elevated temperature, i.e. 4 and 37 degrees C, improved stability of CTX was observed in EDTA plasma samples compared to serum.'] Are serum and plasma fragments of C-telopeptides of type I collagen ( CTX ) stable during storage at low temperatures for 3 years?