Carbon recycling and desaturation and elongation of linoleate, alpha-linolenate and docosahexaenoate in ten fetuses and two nursing infants of chow-fed rhesus monkey mothers were studied in vivo using uniformly labeled tracer molecules and high precision mass spectrometry. Doses of [U-13C]-18:2n-6, [U-13C]-18:3n-3 or [U-13C]-22:6n-3 free fatty acids were infused intravenously to the adults, and milk, maternal plasma, fetal plasma and tissues, and infant plasma were analyzed for enrichment in fatty acids of length C14 to C22. Conversion of tracer fatty acids to palmitic, stearic, oleic, and long chain polyunsaturated fatty acids was observed in fetal liver, brain, and retina ca. 5 days after dosing, and in milk and infant plasma 1 and 7 days after dosing. Animals dosed with [U-13C]-22:6n-3 accumulated more label in the fetal organs compared to the animals dosed with [U-13C]-18:3n-3 or [U-13C]-18:2n-6. The greatest fractions of doses were found in the fetal brains at levels of 0.21%, 0.24% and 1.7% for the [U-13C]-18:2n-6, [U-13C]-18:3n-3, and [U-13C]-22:6n-3, dosed mothers, respectively. Label was found in saturated and monounsaturated fatty acids in liver, brain and retina (0.05-1.5 ppm dose/mg lipid) for all doses. These results demonstrate that 1) recycling of carbon from 18:2n-6, 18:3n-3, and 22:6n-3 into saturates and monounsaturates is a major metabolic pathway in chow-fed primates in the perinatal period; 2) less than 2% of the n-3 doses are found in brain fatty acids of developing fetuses from chow-fed mothers; and 3) [13C]-22:6n-3 accumulates in retina and brain at an order of magnitude higher level when provided as preformed [13C]-22:6 n-3 compared to [13C]-18:3n-3.