The aim of the present study was to quantify the incorporation of eicosapentaenoic acid (epa) and docosahexaenoic acid (dha) into plasma lipids after oral administration of n-3 fatty acid ethyl esters, since little is known about the rate and pattern of incorporation into plasma lipid fractions. In addition, we aimed to obtain preliminary information regarding epa half-life, which is needed to establish an optimal dosing schedule. Five healthy volunteers ingested two 8·5 g doses of n-3 fatty acid ethyl esters daily for 7 d, supplying 6·0 g epa/d and 5·3 g dha/d. The fatty acid compositions of plasma phospholipids (pl), cholesteryl esters (ce) and triacylglycerols (tag) were determined during supplementation and during a washout period of 7 d. Half-lives of epa and dha were calculated. The proportion of epa in pl showed a 15-fold increase after 7 d (p <0·001), while dha showed a smaller increase (p <0·01). In ce, epa also increased (p <0·05), while dha did not increase at all. Remarkably, incorporation of dha into tag was even higher than that of epa. Half-life of epa in pl ranged from 1·63 to 2·31 d (mean 1·97 (se 0·15) d), whereas mean half-life of epa in ce was 3·27 (se 0·56) d. In three subjects, washout of epa and dha from tag seemed to follow a bi-exponential pattern, with a short half-life (<1 d) in the initial phase and a half-life of several days in the second phase. In conclusion, epa ethyl esters are rapidly incorporated into plasma lipids, especially into pl. The relatively long half-life of epa in plasma would permit a dosing schedule with intervals of =12 h in supplementation studies.