The spatial evolution of the spectral exponent of magnetic field fluctuations in the solar wind is investigated by a comparison of spectra and length functions obtained from Helios for in-ecliptic and from Ulysses for high-latitude observations. A similar radial evolution trend is found in both data sets for the Bz component of the magnetic field, which is least affected by compressive interactions. Yet the fluctuations seem to evolve more slowly in the polar flows as compared with the Alfv¿nic fluctuations found by the Helios experiments in coronal-hole-related flows near the Sun in the ecliptic plane. ¿ American Geophysical Union 1996