A rapid and convenient procedure for the quantitative determination of the fatty acid composition of plasma lipids is described. Human plasma was applied directly to the preadsorbent zones of thin-layer silica gel plates with added antioxidant, internal standards and carriers. The thin-layer chromatography (TLC) plates were partially developed with methanol followed by chloroform/methanol (1:1, v/v), and then they were fully developed in hexane/diethyl ether/acetic acid (80:20:1, v/v/v) to separate the major classes of lipids. Silica gel from regions containing the separated lipids was scraped into screw-capped tubes and treated with boron trifluoride-methanol prior to gas chromatography. The method of direct application to TLC plates gave yields and compositions of fatty acids very similar to the method of applying extracted plasma lipids. This relatively simple method is suitable for analyzing the fatty acids in plasma lipids from a 50 microliter finger-tip blood samples from an individual, and it may be useful in wide-scale screening of different individuals to estimate the relative amounts of ingested polyunsaturated fatty acids.