High-resolution (125 m) profiles of cloud condensation nucleus (CCN) number concentration at 1.0% supersaturation were measured 12 times at Laramie, Wyoming (41 ¿N), and twice at Lauder, New Zealand (45 ¿S), extending from the surface to 200 mbar. The balloon-borne instruments included a condensation nucleus (CN) counter to measure particles with diameter greater than ~10 nm and an optical particle counter to measure particles with diameter >0.3 μm (D0.3). Within vertical profiles, variations in CCN concentration were typically positively correlated with changes in CN and D0.3 concentrations and often corresponded with changes in relative humidity, typically positively, but occasionally negatively correlated. The aerosol profiles generally show several distinct layers that can be defined by equivalent potential temperature and relative humidity. These layers are used to summarize the 14 vertical profiles by classifying aerosol measurements into five distinct atmospheric layers: surface, lower tropospheric, upper tropospheric, stratospheric and regions of high humidity. Laramie summer and winter profiles show that the mean CCN concentration decreases between the lower and upper tropospheric layers (450 to 130 cm-3 in summer, 150 to 65 cm-3 in winter). The average summer CCN/CN ratio in Wyoming shows an increase from 0.09 in the lower troposphere to 0.17 in the upper troposphere. The summer CCN concentrations at Lauder, New Zealand, were about twice the summer CCN concentrations measured at Laramie, Wyoming, while the CN and D0.3 concentrations were approximately the same. ¿ 2001 American Geophysical Union