A solution calorimeter was constructed with a temperature range of one degree in the region of 25°C. The precision of the calorimeter was about 0.3%. The heats of reaction of the following silver ethylenediamine complexes were measured: Ag(en)⁺, Ag₂(en)₂⁺⁺, Ag(en)₂⁺, and AgHen⁺⁺. With the formation constants determined by Schwarzenbach (6), the respective entropies were calculated. Enthalpy and entropy data for the Ag(en)⁺, Ag₂(en)₂⁺⁺, and Ag(en) ₂⁺ complexes are reasonable. The data for the AgHen⁺⁺ complex seems anomalous.