The first wintertime spectroscopic measurements of HCI in the Antarctic stratosphere have been made, using the moon as a light source. These measurements have been presented in conjunction with lunar measurements of HNO3, solar measurements of both gases, and meteorological data, allowing a picture of the evolution of the trace gases during 2003 to be developed. The measurements have provided verification of our current understanding of winter processes, including the formation of polar stratospheric clouds, the conversion of HCI to active forms of chlorine, and the redistribution of nitrogen trace gases within the stratosphere. The springtime deactivation of chlorine has also been clearly demonstrated, with measurements of CIONO2 used to investigate chlorine repartitioning at this time. Measurements of HNO3 have been broken down into narrow altitude regions and used to demonstrate denoxification, denitrification, and nitrification processes, as well as the ability of FTIR measurements to produce height-resolved data. The HCI and HNO3 measurements have also been compared to the chemical transport model SLIMCAT, showing generally good agreement, although this was limited by the equilibrium treatment of polar stratospheric cloud formation in the model. Finally, winter measurements of HNO3 have been combined with lidar observations of polar stratospheric clouds, allowing an estimate of the rate of HNO3 uptake to be determined and demonstrating a clear link between HNO3 fluctuations and the phase of the clouds. A link between brief anomalous increases in the gas phase HNO3 during otherwise denitrified conditions and large nitric acid-containing particles has also been proposed.