The on-line analysis of gas streams containing ultra low-level concentrations of CO2over extended time periods presents a unique analytical problem. In the absence of a CO2preconcentration step, many commercially available instruments used for routine gas analysis lack either the sensitivity or stability for ultra low-level CO2monitoring. This paper will address two relatively inexpensive (<$10,000) techniques that were found suitable for such monitoring: (1) CO2methanization with subsequent flame ionization detection and (2) extended-pathlength infrared spectroscopy.