Magnetic susceptibility, resistivity, specific heat, and thermoelectric power measurements on EuCu2Si2, YbCu2Si2, CeCu2Si2, and GdCu2Si2 are presented. The first three compounds show a demagnetization of the 4f shell, while the fourth was studied to determine the “normal” magnetic and electronic properties for the RE-Cu2Si2 system. YbCu2Si2, CeCu2Si2, and EuCu2Si2 are found to exhibit similar lattice, electronic, and magnetic properties: an intermediate lattice constant; a magnetic susceptibility that is large and paramagnetic but neither shows order nor a Curie divergence; a large electronic specific heat coefficient; strong deviations from a simple T law in the high-temperature resistivity; and a large maximum in the thermoelectric power. The data are interpreted in terms of interconfiguration fluctuations (ICF), and a simple model is presented which can quantitatively explain the magnetic susceptibility and semiquantitatively predicts the specific heat. In addition, the model is in qualitative agreement with the resistivity and thermoelectric power data.