Capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) was used to analyze a 50-microliters sample of cerebrospinal fluid from leukaemic children treated with high doses of methotrexate. Free amino acids and primary amines are labelled with fluorescein isothiocyanate prior to analysis. Electropherograms containing more than 50 peaks were obtained in less than 22 min. Twenty-one peaks were identified, and 19 were quantitated. Observed differences in individual amino acid levels are compared with healthy reference values. The results indicate that CE-LIF is useful as a selective, rapid and sensitive tool for the determination of free amino acids and amines in clinical biology studies.