The seed oils from twenty-five Conifer species (from four families-Pinaceae, Cupressaceae, Taxodiaceae, and Taxaceae) have been analyzed, and their fatty acid compositions were established by capillary gas-liquid chromatography on two columns with different polarities. The oil content of the seeds varied from less than 1% up to 50%. Conifer seed oils were characterized by the presence of several Delta 5-unsaturated polymethylene-interrupted polyunsaturated fatty acids (Delta 5-acids) with either 18 (cis-5, cis-9 18:2, cis-5, cis-9, cis-12 18:3, and cis-5, cis-9, cis-12, cis-15 18:4 acids) or 20 carbon atoms (cis-5, cis-11 20:2, cis-5, cis-11, cis-14 20:3, and cis-5, cis-11, cis-14, cis-17 20:4 acids). Pinaceae seed oils contained 17-31% of Delta 5-acids, mainly with 18 carbon atoms. The 20-carbon acids present were structurally derived from 20:1n-9 and 20:2n-6 acids. Pinaceae seed oils were practically devoid of 18:3n-3 acid and did not contain either Delta 5-18:4 or Delta 5-20:4 acids. Several Pinaceae seeds had a Delta 5-acid content higher than 50 mg/g of seed. The only Taxaceae seed oil studied (Taxus baccata) had a fatty acid composition related to those of Pinaceae seed oils. Cupressaceae seed oils differed from Pinaceae seed oils by the absence of Delta 5-acids with 18 carbon atoms and high concentrations in 18:3n-3 acid and in Delta 5-acids with 20 carbon atoms (Delta 5-20:3 and Delta 5-20:4 acids). Delta 5-18:4 Acid was present in minute amounts. The highest level of Delta 5-20:4 acid was found in Juniperus communis seed oil, but the best source of Delta 5-acids among Cupressaceae was Thuja occidentalis. Taxodiaceae seed oils had more heterogeneous fatty acid compositions, but the distribution of Delta 5-acids resembled that found in Cupressaceae seed oils. Except for Sciadopytis verticillata, other Taxodiaceae species are not interesting sources of Delta 5-acids. The distribution profile of Delta 5-acids among different Conifer families appeared to be linked to the occurrence of 18:3n-3 acid in the seed oils.