delta C-13 values of a suite of halocarbons have been determined in an urban background site in Bristol, UK. A novel mobile preconcentration system, based on the use of multi-adsorbent sample tubes, has been developed for trapping relatively large-volume air samples in potentially remote areas. An Adsorption Desorption System-Gas Chromatography Electron Capture Detector was used to measure the mixing ratios of the selected halocarbon species, while a Gas Chromatography-Combustion-Isotope Ratio Mass Spectrometer was used to determine delta C-13 values. For the species with strong local sources, the variation of isotope ratios has been observed over the experimental period. Some of the results reported in the present study differ from previously reported values and reasons for this are discussed. The reporting of different delta C-13 values for selected halocarbons from different areas in the present study suggests that delta C-13 values may be used to determine the relative magnitudes of anthropogenic and biogenic sources.