Hollow fibre-protected liquid-phase microextraction (HF-LPME) together with gas chromatography-mass spectrometry was, for the first time, investigated for the in-situ derivatisation and analysis of basic degradation products of chemical warfare agents in water samples. The degradation products studied were those of nerve and blister agents, and a psychotomimetic agent. Extractions with in-situ derivatisation were successfully performed using a mixture of solvent and derivatising agent. The protection of the moisture-sensitive derivatising agent was afforded by the hydrophobic hollow fibre. Parameters such as type of derivatising agent, extraction solvent, pH, salt concentration, stirring speed and extraction time were optimised using spiked deionised water samples. The linear range established was between 0.05 and 25 microg ml(-1) depending on analyte, with squared regression coefficients ranging from 0.9959 to 0.9996. Relative standard deviations (RSDs) ranged from 6% to 10%. As comparison, solid-phase microextraction (SPME) was also evaluated and extraction conditions such as pH, salt concentration, stirring speed and extraction time were optimised. This work also represented the first report of such an in-situ derivatisation approach for SPME of basic analytes. The linear range established was between 0.5 and 25 microg ml(-1) depending on analyte, with squared regression coefficients ranging from 0.9946 to 0.9998. RSDs ranged from 5% to 22%. The limits of detection of HF-LPME (0.04-0.36 microg l(-1)) showed improvement over those of SPME (0.06-0.77 microg l(-1)).