Current evidence suggests that at least part of the cardioprotective benefits of consumption of long-chain n-3 polyunsaturated fatty acids (PUFAs) relates to their incorporation into the phospholipids of cardiac cell membranes. Dietary supplementation with purified extracts of n-3 PUFAs derived from fish oil rapidly alters the composition of fatty acids in blood cell membranes and in other tissues. The present review summarises the time-course and dose-dependent incorporation and washout of n-3 PUFAs in the clinical setting and discusses the implications of these pharmacokinetic data in terms of biological effects.