Two methods are described, both currently used in our laboratory, for the quantitative analysis of very long-chain fatty acids, phytanic acid and pristanic acid in plasma and cultured fibroblasts by gas-liquid chromatography. The first method is based on the procedure developed by Moser and Moser (1991) and the second is based on the method of Onkenhout and colleagues (1989), which is an application of the original method of Lepage and Roy for plasma and fibroblasts. A survey is given of the concentrations of very long-chain fatty acids, pristanic and phytanic acid in plasma and fibroblasts from control subjects and all patients investigated so far in our laboratory.