1. For identical concrete compositions and temperature and moisture regimes of its aging, the modulus of elasticity in the mass of the structure and large laboratory specimens prepared without screening out the coarsest aggregate agree closely. 2. The investigative method presented permits obtaining reliable data on the modulus of elasticity of concrete within a structure with eight times less labor cost than in laboratory testing of large specimens. 3. Between the experimental values of Emax and Emin of concrete in the mass there are differences reaching ±13% of the average value of Eav, which is probably related with qualitative and quantitative changes in the concrete components during the long-term period of dam construction. Therefore, in the strain-gauge method of studying the state of stress in a structure at full scale it is recommended to use not the averaged modulus of elasticity for the entire mass but the values of E obtained in the immediate vicinity of the straingauge rosette at each level.