According to predictions from the current theoretical models for ageing the heterogeneity of the population is increasing with increasing age. Although the direct observation of such changes in humans is extremely difficult, supporting evidence should be identifiable in key biomarkers associated with health and mortality. Using data from the Northwick Park Heart Study II of 3052 healthy middle-aged men (mean 56 years of age, range 49-69 years), with 5 annual measures of CHD risk factors, ageing effects were tested for plasma fibrinogen, cholesterol and triglycerides. Fibrinogen levels increased with age (p < 0.0001), while cholesterol showed a decrease, and triglycerides did not show any change with age. There was a significant increase in the variance of fibrinogen with age (p < 0.0007) but not for cholesterol or triglycerides. The raising effect on fibrinogen levels associated with the A allele of the FIBB - 455G>A promoter variant also decreased with age (p = 0.005). The age-associated changes observed in the fibrinogen variability and the association of phenotype to genotype are discussed in light of the evolutionary theory, and their implications are considered.