The 1984 extratropical mission of NASA's Stratosphere-Troposphere Exchange Project (STEP) studied cross-jet transports in regions of cyclogenesis and tropause folding. Correlations of 7Be, ozone, water vapor, and potential vorticity measured on a NASA U-2 research aircraft flying in high shear regions above the jet core are indicative of mixing between the cyclonic and the anticyclonic sides of the jet and are consistent with the hypothesis that small-scale entrainments of upper tropospheric air into the lower stratosphere during cyclogenesis are important in maintaining the vertical gradients of 7Be, ozone, water vapor and other trace constituents in the lower few kilometers of the mid-latitude stratosphere. Correlations between 7Be and ozone suggest a lower tropical stratospheric origin for the ozone-poor lamina observed above the jet core. ¿American Geophysical Union 1991