['Blood cholesterol levels are affected by diet and in particular by the type of fat intake. We originally showed that a significant but variable amount of cholesterol is firmly bound to haemoglobin (Hb) yielding the Hb-lipid adduct (Hb-Ch) in erythrocytes isolated from normo-lipidemic males.', 'To establish whether dietary lipids affect the level of Hb-Ch in human erythrocytes.', 'Seventy-four healthy free-living adults were separated according to their serum cholesterol levels into two groups: normo-cholesterolemic (LDL cholesterol <3.4 mmol/l and total cholesterol <5.2 mmol/l) (NC) and hyper-cholesterolemic (LDL cholesterol >or=3.4 mmol/l) (HC). Habitual dietary information was used to classify subjects in both study groups into sub-groups of low-fat (<or=30% total energy as fat) and high-fat consumers (>30% total energy as fat). The NC low-fat consumers were placed on a high-lipid (high-fat and high-cholesterol) diet whereas the HC subjects with high-fat intake were assigned to a low-lipid (low-fat and low-cholesterol) diet. Both types of dietary intervention were allowed to continue for 6 weeks. The main variable under scrutiny was the Hb-Ch concentration.', 'In both study groups low-fat intake subjects had low levels of Hb-Ch (approx. 0.35 mmol/l RBC) compared with high-fat intake subjects (approx. 0.60 mmol/l RBC), and serum cholesterol was not correlated with Hb-Ch. The two dietary interventions produced substantial changes in the Hb-Ch level that paralleled variation in the serum cholesterol concentration. A high-lipid diet (35% fat, 15% saturated; 580 mg cholesterol) increased Hb-Ch (by approximately 47%, P<0.001) in subjects with low Hb-Ch at onset, whereas a low-lipid diet (28% fat, 9% saturated; 280 mg cholesterol) decreased Hb-Ch (by approximately 40%, P<0.001) in subjects with high Hb-Ch at onset.'] Does dietary lipid intake influence the level of cholesterol bound to haemoglobin in human erythrocytes?