Soluble solids content (SSC) and Magness-Taylor flesh firmness (MTO of "Hayward" kiwifruits were non-destructively assessed by means of a waveguide, that houses the fruit, connected to a sweeper oscillator and a spectrum analyzer. A preliminary test was conducted with a plastic fruit filled with solutions with different SSC values in the frequency range from 2 to 20 GHz (with a step of 1 GHz). The best linear correlations (R(2) up to 0.987) between electric signals and SSC solutions in the above described test were found in the 2-3 GHz and 15-16 GHz steps. These steps were used for the dielectric measurements on kiwifruit samples during storage of 28 days at 14 degrees C. Partial least squares (PLS) regression were then used to predict SSC and MTf from these acquired spectra. In "test set" validation. PLS models showed R(2) values up to 0.804 (RMSE = 0.98 degrees Brix) and 0.806 (RMSE = 8.9 N) for the prediction of SSC and MTf, respectively. (C) 2011 Elsevier Ltd. All rights reserved.