Condensation nuclei (CN) were measured in the free troposphere (FT) above the Jungfraujoch (JFJ) high-alpine research station (3454 m; Switzerland) from 4.5 to 12 km asl in a case study on July 30, 1997. Vertical profiles of CN concentration for d≥5 nm(N≥5), d≥15 nm(N≥15) were measured, and indicated that ultrafine CN (UCN; 5≤d≤15 nm;N5--15) exhibited a distinct increase with altitude. Some evidence for near-constant values of d(log CN)/dz within discrete layers was found, which generally coincided with different airmasses as delineated by changes in the lapse rate d&thgr;/dz at ~5.5, 6.4, 9.0 and 10.6 km asl. In addition, CN concentration was mapped over a 40¿75 km horizontal domain at 8.0 km asl centered above the JFJ. A pronounced variation in N≥5, N≥15 and specific humidity, but not in UCN, exhibited quasi-stationary 2-D features and was attributed to the chance encounter of a mountain wave. The case study provides further evidence that the upper FT may be a source of new particles. ¿ 1999 American Geophysical Union