Headspace solid-phase microextraction (HS-SPME) analysis of low-molecular mass (C1-C10) aldehydes in aqueous solutions was investigated, using pentafluorophenylhydrazine (PFPH) and o-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) as in-fibre derivatisation reagents. Analysis of the derivatives was achieved, using GC-flame ionisation detection (FID). A comparison of the two reagents showed that PFBHA was superior to PFPH under the investigated conditions. Fundamental studies of the PFBHA and PFPH reactions showed that the kinetics of the process was limited by the mass transport rate of the analytes to the fibre. The developed PFBHA method gave detection limits in the low to sub-microgram per litre range for most of the aldehydes tested. The method was applied successfully to the analysis of particleboard, wine and fish samples.