Several biological thiols (cysteine, homocysteine and glutathione) together with their disulphides (cystine, homocystine and oxidized glutathione) could be simultaneously determined by micro liquid chromatography (LC) with fluorescence detection. Based on an existing procedure, the samples were first treated with the thiol-specific fluorigenic reagent ABD-F followed by disulphide reduction with tributyl-phosphine and SBD-F derivatization of the reduced disulphides. Different mobile phases, columns, injection volumes and detection systems were tried for the optimization of the separation. Quantitative studies gave detection limits at the picogram level per 60-nl injection volumes. Calibration graphs were linear with correlation coefficients >0.999. The possibility of applying gradient elution to this system represents an advantage over high-performance thin-layer chromatographic assays. Likewise, the advantages of micro-LC over classical high-performance liquid chromatography may contribute to the choice of the most suitable system depending on the analytical requirements.