We use the ratio between cosmogenic radionuclides beryllium 10 (t1/2=1.5¿106 years) and beryllium 7 (t1/2=53 days) to study stratospheric transport, particularly the exchange between the tropics and the high latitudes and as an indicator of stratosphere-troposphere exchange. Both tracers are generated steadily, with maximum production occurring at midlatitudes of the stratosphere. During transport away from their source the ratio 10Be/7Be increases and thus acts as a clock for air mass age. According to model (GISS GCM) calculations, the tropics is a reservoir of high-ratio air with the high magnitude of 10Be/7Be partly a consequence of air mixed in from higher latitudes. The observations of Dibb et al. <1994> show a vertical maximum in 10Be/7Be in the lower arctic stratosphere during the spring of 1989; model results qualitatively reproduce this maximum and suggest that it may result from transport of tropical air to high latitudes during winter. The model ratio values are not so large as in these observations, possibly due to either excessive leakage into the troposphere near the pole or to insufficient transport from the tropical stratosphere to the pole. Beryllium 10 and 7Be observations, combined with model analysis, can be a useful indicator of transport processes in the troposphere/stratosphere system. ¿ 1998 American Geophysical Union