A gas diffusion-flow injection system was developed for the determination of carbon dioxide in gaseous samples. The calibration was based on the use of either gaseous carbon dioxide or aqueous sodium carbonate standards. Gaseous carbon dioxide samples and gaseous or aqueous standards were injected directly into a donor stream of 1.0x10(-4)M H(2)SO(4). In the gas diffusion unit, carbon dioxide diffused through a PTFE membrane into an acceptor stream containing a mixed acid/base indicator. The absorbance of the acceptor stream was monitored spectrophotometrically at 554nm. The calibration plot was linear over the range of 5.00x10(2) to 1.27x10(4)mull(-1) with a sample throughput of 28h(-1) and 3.2% R.S.D. ([CO(2)]=2.37x10(3)mull(-1), n=12). The detection limit was determined as 2.50x10(2)mull(-1). The flow system was successfully applied to the analysis of several natural gaseous samples and the headspace of milk containers during storage. The flow injection results were found to be statistically indistinguishable at the 95% confidence level from those obtained by gas chromatography using thermal conductivity detection.