Chemical ozone depletion during the unusually cold 1994--1995 Arctic winter is quantified using ozone profile measurements from the space-based Polar Ozone and Aerosol Measurement (POAM II) instrument and the REPROBUS three-dimensional chemistry transport model. The model is first used to determine the dynamical component of the observed variations, allowing the chemical component to be quantified from the observations. This technique has been previously used to estimate ozone loss from ground-based total column measurements. In the present study, it has been adapted to the POAM II vertical profile measurements in order to document the vertical evolution of ozone chemical loss throughout the winter both inside and outside the polar vortex. The cumulative ozone loss thus obtained inside the vortex at the end of the winter is found to reach a maximum of 51% (with respect to the REPROBUS dynamics-only prediction) at the 430 K potential temperature level. The largest ozone depletion rates were observed in late January when record low temperatures were reported, and the vortex was largely displaced towards midlatitudes. The maximum depletion rate was 1.4%/d occurring at the 470 K potential temperature level. Smaller but significant chemical ozone depletion was also found outside the vortex, where cumulative ozone losses of 19% were observed in the lower stratosphere. Finally, comparison of chemical ozone loss inferred from the POAM measurements with that obtained from the REPROBUS model indicates that the model underestimates cumulative ozone loss inside the vortex (by ~30% in the lower stratosphere). ¿ 1998 American Geophysical Union