To find an appropriate dietary supplement for pregnant women that would enhance their docosahexaenoic acid (DHA, 22:6n-3) status, without decreasing the n-6 long-chain polyenes (LCP) status, both in plasma and in erythrocyte phospholipids, a dose-finding study was performed in healthy non-pregnant women. Six groups of non-pregnant women received daily over a 4-week period one of the following supplements: tuna fish oil (0.266g/d or 0.532 g/d DHA), single cell-derived oils containing either DHA alone (0.285g/d or 0.570 g/d) or DHA and arachidonic acid (AA, 20:4n-6; 0.570 g/d DHA and 0.259 g/d AA). A control group received a placebo containing microcrystalline cellulose. Fatty acids were analyzed in plasma, and erythrocyte phospholipids of the blood samples collected weekly. After 4 weeks of supplementation, the levels of DHA and n-6 LCP of the control group were unchanged. In the other groups, the levels of DHA were significantly and dose-dependently increased as compared to those in the control group. Significant reductions were found in the levels of n-6 LCP, except in the group that received the mixture of DHA and AA enriched single cell oils. So, only this latter mixture was effective in increasing the levels of DHA and preventing an n-3 induced reduction in n-6 LCP. Whether this supplement effect will be the same in pregnant women needs further investigation.