Very valuable information can be obtained by studying surface chemical abundances in stars with orbiting planets. Possible interactions between extrasolar planets and their parent stars can be studied using light elements as lithium and beryllium, which are excellent tracers of mixing mechanisms operating in the stellar interior. A wide sample of stars hosting planets, with spectral types in the range F7V-K0V, have been observed and their beryllium abundances derived to study in detail the effects of planets on the structure and evolution of their associated stars. Preliminary results suggest that either low-mass planet hosts are anomalously beryllium depleted stars, or theoretical evolutionary models have to be revised for stars with effective temperatures below ˜ 5600 K.