Mass-independent fractionation (MIF) of ozone has been observed in both the troposphere and stratosphere. Because ozone is a photochemically active species, its MIF signature can be imparted to other atmospheric molecules. Using a photochemical equilibrium model for short-lived radical species, I have computed the expected MIF for typical mid-latitude conditions. The model accounts for about ~70% of recent measurements of Δ17O for H2O2 in rainwater, and predicts large MIF for NOx and ClO species (~40--70?), and their products (ClONO2 and HNO3). Furthermore, in the stratosphere oxygen exchange reactions between OH and NOx yield OH with Δ17O from 2 to 45?. Stratospheric water produced during H abstraction by OH would be similarly mass-independently fractionated. In the troposphere rapid exchange between OH and H2O erases any MIF signature in OH. These model results depend on several O exchange reactions with unknown activation energies or with rate coefficients known only as upper limits. ¿ 2001 American Geophysical Union