Despite the importance of human milk fatty acids for infant growth and development, there are few reports describing infant intakes of individual fatty acids. We have measured volume, fat content and fatty acid composition of milk from each breast at each feed over a 24 h period to determine the mean daily amounts of each fatty acid delivered to the infant from breast milk at 1, 2, 4, 6, 9 and 12 months of lactation in five women. Daily (24 h) milk production was 336.60 (SEM 26.21) and 414.49 (SEM 28.39) ml and milk fat content was 36.06 (SEM 1.37) and 34.97 (SEM 1.50) g/l for left and right breasts respectively over the course of the first year of lactation. Fatty acid composition varied over the course of the day (mean CV 14.3 (SD 7.7) %), but did not follow a circadian rhythm. The proportions (g/100 g total fatty acids) of fatty acids differed significantly between mothers (P<0.05) and over the first year of lactation (P<0.05). However, amounts (g) of most fatty acids delivered to the infant over 24 h did not differ during the first year of lactation and only the amounts of 18:3n-3, 22:5n-3 and 22:6n-3 delivered differed between mothers (P<0.05). Mean amounts of 18:2n-6, 18:3n-3, 20:4n-6 and 22:6n-3 delivered to the infant per 24 h over the first year of lactation were 2.380 (SD 0.980), 0.194 (SD 0.074), 0.093 (SD 0.031) and 0.049 (SD 0.021) g respectively. These results suggest that variation in proportions of fatty acids may not translate to variation in the amount delivered and that milk production and fat content need to be considered.