Specific heat measurements of (Gd1-xYx)(3)T compounds (T= Co and Ni) revealed a strong concentration dependence of the coefficient gamma of the T-linear specific heat. In particular, the electronic specific heat coefficient gamma Of Y3CO was found to be significantly lower (15 mJ/molK(2)) than that of isostructural Gd3Co (110 mJ/molK(2)) and (Gd0.2Y0.8)(3)CO (380 mJ/molK(2)). Such a behaviour can be attributed to the presence of a huge contribution of spin fluctuations in the d-electron subsystem induced by the f-d exchange interaction.