In order to measure vertical particle fluxes, a condensational particle counter (CPC) has been adapted to operate together with an ultrasonic anemometer as an eddy covariance (EC) measurement system. Application of the CPC in the EC unit extends the size interval of particles included in flux measurements down to 12 nm (50% cut-off size diameter). A sample of particle-flux measurements obtained over a 12 m high Scots pine forest at the SMEAR II field measurement station in Southern Finland (61 degrees 51＇N, 24 degrees 17＇E) in August 1996 is presented. The operation of the system is studied by analysing spectra and co-spectra of turbulent records which demonstrate the suitability of CPC in the EC system. Data show the extended periods of upward fluxes probably due to the formation of new particles below the measurement level, possibly inside the canopy. The observed fluxes normalised with concentration are in a reasonable agreement with earlier studies.