Unsaturated C20 fatty acids from bovine lens have been examined via gas chromatography-mass spectrometry of their pyrrolidide derivatives. The presence of arachidonic acid and 5,8,11-20:3 in bovine lens has been confirmed by this study. In addition, the 10-, 11-, 12-, and 13-isomers of 20:1 and the 7,13-, 18,14-, and 12,15-isomers of 20:2 were identified.