Several physical properties were measured for two zinc phosphate and three polycarboxylate cements. The specimens were tested in compression 24 h after they had been made. Two series of specimens were examined. In one series the cement powders were given a correct treatment, protected from atmospheric humidity. In the other series the powders were exposed for 1 week to ambient conditions with the temperature varying between 20°and 24°C and the relative humidity between 40% and 59%. The zinc phosphate cements were characterized by high values of modulus of elasticity and by plastic deformations less than 0.2%. The polycarboxylate cements were more flexible and also exhibited large plastic deformations. Compared with the zinc phosphate cements, therefore, the polycarboxylate cements had high values of resilience and toughness. The storing of cement powders exposed to atmospheric humidity for 1 week did not change the measured properties of the polycarboxylate cements. However, both strength and resilience were significantly reduced for one phosphate cement.