A new method of estimating the downward ozone flux across the midlatitude tropopause is introduced. The algorithm derives the estimate from total column ozone observations. Vertical information is given by analysis potential vorticity fields. This method yields an annual estimate of 500 ¿ 140 Tg yr-1 stratospheric injection of ozone into the northern hemisphere, midlatitude troposphere. The downward ozone flux exhibits the expected spring maximum and autumn minimum. The annual distribution of the cross-tropopause ozone transport by latitude is consistent with the seasonal frequency and distribution of baroclinic systems. This algorithm also produces localized results and can thus be applied to a single case or global studies.