Underivatized fatty acids occurring in lipids of a number of biological specimens (blood plasma, tissues, food) were studied using a capillary column with a chemically bonded free fatty acid phase and a programmed temperature vaporizer. Non-linear calibration dependences were obtained for almost all the acids at lower concentrations because of losses in the column, non-linearity increasing with increasing carbon number and degree of unsaturation. Sample introduction at temperatures below the solvent boiling point eliminates losses in the injector. The lower recovery of long-chain polyunsaturated acids is caused by interactions occurring in the column. Some critical pairs remain unresolved in the underivatized form (18:1n9-18:1n7, 20:4n6-20:3n3), whereas the corresponding methyl esters exhibit baseline resolution.