A least squares data reduction technique for extracting stratospheric ozone abundances concurrently with NO2 abundances is described. The observational technique used is ground based long path absorption spectroscopy in the wavelength range 435-450nm. Sources of error are discussed and the overall accuracy of ozone retrievals is quantified in terms of the maximum residual errors accepted. Results obtained from our clean air site at Lauder New Zealand (-45 ¿S, 170 ¿E) are presented for the period December 1980 to April 1982, and compared with Dobson total ozone values. Although less accurate (~¿20%) than the Dobson values, the technique may find use because both NO2 and O3 amounts are obtained simultaneously from the same sampled volume. Thus there is the potential for providing observational evidence for modelled coupling between these two species.