A crossover study was designed to determine whether the fat and carbohydrate contents of evening meals consumed the night preceding glycaemic index (GI) testing had an effect on the GI. Twenty participants consumed two different evening meals in which the energy contributions from fat, carbohydrate and protein were in the ratio 50:30:15 and 25:60:15, respectively. Each participant completed eight tests that involved two evening meals with different macronutrient compositions followed the next morning by two treatments, glucose beverage or fruit bread, all carried out in duplicate. The GI of fruit bread was determined on the mornings following each of the evening meals. The GIs (95% CI) were 68 (60, 76) and 59 (52, 67) after the high-carbohydrate and high-fat meals, respectively, and were not different (P=0.11). Thus, varying the fat and carbohydrate contents of the evening meal before GI testing the next morning did not affect the GI.