In-situ GC analysis of SF6 and halofluorocarbons in the atmosphere was achieved by sampling a measured volume of ambient air through a short adsorption tube, or precolumn, from which the collected vapours were released by heating and then transferred directly by the carrier stream to the analytical column. The collection, transfer and analysis operations were performed in the one instrument with the aid of gas sampling valves, thereby minimizing the risk of loss or contamination associated with other sample storage and removal procedures. Field trials using CBr2F2 and SF6 as tracers have demonstrated the efficacy of the technique for the quantitative measurement of such gases in the atmosphere. The detection limit attained in this work is estimated to be about 5¿10-14 v/v.