The most abundant long-chain polyunsaturated fatty acid in brain and retinal lipids is docosahexaenoic acid (DHA, C22:6 omega 3). It becomes incorporated into nerve tissues mostly in utero and during the 1st yr of life. DHA is derived in humans either performed in the diet or by hepatic synthesis from dietary linolenic acid (C18:3 omega 3). Since human milk contains DHA, this study was designed to see if increased dietary DHA would be reflected in a higher DHA content in human milk. Eight lactating women were given supplements of a fish oil concentrate rich in omega-3 fatty acids, including DHA (11% of fatty acids). Six women took 5 g/day of fish oil for 28 days; five women consumed 10 g/day for 14 days; and one woman consumed 47 g/day for 8 days. Each intake level of fish oil produced significant dose-dependent increases in the DHA content of milk and plasma. Base-line DHA levels in milk were 0.1 +/- 0.06% of total fatty acids. Five g/day of fish oil raised the levels to 0.5 +/- 0.1% (p less than 0.001); 10 g/day raised DHA levels to 0.8 +/- 0.1% (p less than 0.001); and 47 g/day produced DHA levels of 4.8%. The results of this study indicated that relatively low intakes of dietary DHA significantly elevated milk DHA content. This would clearly elevate the infant's DHA intake and might have implications for brain and retinal development.