In one study a group of 10 young adult male volunteers were given two experimental diets, differing in fat content. In a second study another group of 12 such volunteers received two experimental diets differing in linoleic acid content. The retention of calcium, magnesium and iron was measured during the dietary periods, each lasting 1 month. Decreasing the fat intake from 42 to 22 energy % did not result in statistically significant changes of the mineral balance. An increase in linoleic acid intake from 4 to 16 energy % (at a constant level of fat intake of 42 energy %) caused a decrease in the iron balance from 3.3 to 2.3 mg/day (p < 0.01), while the calcium and magnesium retention did not change significantly. During the high linoleic acid dietary period haemoglobin levels decreased from 9.6 to 9.1 mmol/l and packed cell volume from 0.48 to 0.461/1 (p < 0.01). This effect of linoleic acid on iron utilization needs further investigation.