Abstract: For the selective enrichment with fatty acids, of which the first double bond is in the 6 position, of a starting material containing fatty acids of which the first double bond is in the 6 or 9 position, the starting material is treated with a saturated solution of urea in methanol with predetermined ratios of fatty acids to urea so as to separate the fatty acids, other than the .DELTA.6 polyunsaturated fatty acids in the form of an insoluble inclusion complex.The enriched fractions obtained may be treated by high-performance liquid chromatography to isolate substantially pure .gamma.-linolenic acid.The enriched fractions, optionally recombined with glycerol, may be used in medicaments and in nutritive compositions or may even serve as starting product in the synthesis of dihomo-.gamma.-linolenic acid.