We studied the effect of a change in dietary fat composition on serum total and high-density lipoprotein cholesterol and growth in healthy infants between 7 and 13 months of age. The intervention families (n = 22) received individualized dietary counselling when the infant was 7, 8 and 10 months of age. The intervention diet was designed to have a fat content of 35-45 E% of total energy intake in infants aged 7-12 months and 30-35 E% after 12 months of age. The ratio of saturated to monounsaturated to polyunsaturated fatty acids was designed to be 1:1:1. The children in the control group (n = 23) were given no specific advice on the fat composition of the diet. Intake of polyunsaturated fatty acids was significantly higher in the intervention group than in the controls (5.9 E% versus 3.6 E%, p < 0.05). Serum total cholesterol concentration decreased significantly in the intervention group during the study from 4.16 +/- 0.41 mmol/l to 3.86 +/- 0,48 mmol/l (p < 0.05). The infants of both groups grew like average Finnish children. Modification of dietary fat composition, as widely recommended for adults and older children to prevent coronary heart disease, decreases cholesterol values in infants without affecting their normal growth.