Systemic infections may thicken the intima of coronary arteries and modify the serum lipid profile. Infants and children are particularly susceptible to such intimal thickening, the signs of which are more pronounced in infants who have evidence of infection at death. The topography of the thickenings, their greater size in males, and in families with a history of coronary heart disease favours the idea that the thickenings are pre-atherosclerotic. Infections modify the serum lipid pattern: serum high density lipoprotein (HDL) cholesterol concentration decreases and stays low during convalescence. Thus repeated infections might prove to be a risk factor for atherosclerosis via their effect on HDL concentration.