It is now possible to measure serum markers of fibrosis in circulating blood. Work in this area has established the reproducibility and reliability of measurements of pro-collagen I and pro-collagen III amino-terminal, secreted as the collagen molecules are released from the fibroblast. These markers have been analysed in several settings, including normal individuals, hypertensive populations and in those with established heart failure due to systolic dysfunction. Recently we have completed a study on analysis of these factors in patients with proven diastolic heart failure. These data have demonstrated an increased activity of the amino terminal pro-collagen III (PIIINP) with a trend towards an increase in the amino-terminal pro-collagen I (PINP). Other relevant markers of the fibrotic process were not altered, including metalloproteinase enzymes (MMP) and tissue inhibitors of metalloproteinase enzymes (TIMP)