Microscale thin-layer chromatography (TLC) of unsaturated fatty acids on silicic acid impregnated with silver nitrate has been employed via the latroscan Chromarods-S with quantitation through the flame ionization detector (FID). The complex mixture of C20 dienoic acids of a partially hydrogenated menhaden oil, with an iodine value (IV) of 84.5, was fractionated with benzene as developing solvent into three groups of increasing Rf; value. The least mobile group was the cis,cis-nonmethylene-interrupted dienes (NMID), followed by the cis,cis-methylene-interrupted dienes (MID) mixed with the cis,trans- + trans,cis-NMID; while the most mobile group included both cis, trans- + trans, cis-MID with the trans, trans-NMID. No trans, trans-MID was detected. Similarly, the C20 monoenoic fatty acids were readily fractionated and quantitated as cis- and trans-isomers. The FID correction factor was greater for the cis- than for the trans-isomers, unexpectedly opposite to the result usually obtained when calculating the FID correction factor in gas/liquid chromatographic (GLC) analyses. This difference in the FID correction factor for the latroscan and the GLC analyses could arise from the types of complexes formed in absorption of the cis- and trans-isomers on the silver nitrate rods.