The primary aim of the trial was to investigate the influence of menopause on the incorporation of marine n-3 PUFA into platelets and adipose tissue. A secondary aim was to evaluate whether marine n-3 PUFA may change levels of circulating oestrogens in women. Ninety-two pre- and postmenopausal women were randomly assigned to consume 2.2 g of marine n-3 PUFA or control oil daily for 12 weeks. Adipose tissue biopsies and blood samples were collected at baseline and after intervention. Eighty-nine women completed the study. Baseline contents of total marine n-3 PUFA and each of the major long-chained n-3 PUFA, EPA, docosapentaenoic acid and DHA were all significantly lower (P < 0.05) in the premenopausal group both in platelets and adipose tissue, except for EPA in platelets (P = 0.05). After supplementation with fish oil, the content of all marine n-3 PUFA increased significantly in platelets and adipose tissue in both pre- and postmenopausal women. The increase in platelets and adipose tissue was, however, the same in both groups. There was no effect of fish oil on oestrogen levels in postmenopausal women. We found a significant difference in premenopausal women, in whom oestradiol (P < 0.04) and oestrone (P < 0.02) serum concentrations increased after the fish oil supplement. This trial did not reveal any difference in the ability of pre- and postmenopausal women to incorporate marine n-3 PUFA into platelets or adipose tissue. However, supplementation with fish oil increased oestrogen levels in premenopausal women.