The form and development of the vertical distribution of ozone are examined during the Antarctic winter and spring by comparing profiles selected from a series of balloon-borne ozonesonde ascents which were launched from Halley Bay in 1987. The progress of the ozone depletion is followed from its onset in late August until the deep minimum in mid-October, when nearly all the ozone has been destroyed between 90 and 50 mbar. The presence of structure in the unperturbed profile is discussed, and it is shown that individual profiles are susceptible to the effects of vertical motion and wind shear. After the spring equinox, the vertical distribution of ozone consistently displays a minimum in mixing ratio, in contradiction to theories which purport to explain the spring development by transport alone. The depletion process is restricted to a finite vertical range of some 12 km, with a sharp upper boundary at about 20 mbar.