We present measurements of the coefficients of linear thermal expansion of single-crystalline samples of the tetragonal heavy-fermion compound

{CeRu}_{2}

{Si}_{2}

, and its nonmagnetic analog

{LaRu}_{2}

{Si}_{2}

, in the temperature range 1.5–270 K. The electronic part of the thermal expansion of

{CeRu}_{2}

{Si}_{2}

yields two distinct anomalies: (1) a huge positive contribution, caused by the (antiferro)magnetic interactions between the quasiparticles, centered at 9 K, and (2) a negative crystal-field contribution centered at 120 K. The data are compared with existing specific-heat data (T<100 K). An analysis in terms of Grüneisen parameters yields the very large value of

Γ_{hf = 190}

for the low-temperature contribution and a value

Γ_{cf = - 5.3}

for the crystal-field contribution. A quantitative analysis using a simple single resonance-level model yields a Kondo-type temperature of 19 K. An analysis of the crystal-field contribution yields a first excited level at 288 K. We also discuss low-temperature scaling behavior by comparing new magnetostriction measurements, that cover the metamagnetic behavior, with magnetization data.

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