In the present paper, the application of the centre hole technique to concrete structures is examined and an efficient scheme developed for the determination of the in-situ stresses. An effective data processing procedure for the complex strain relaxation data is proposed. The variability of concrete as a material makes it necessary to improve on previous techniques, also the high degree of redundancy in the test data must be dealt with. In the proposed procedure, a so-called 'surface stress' is defined which allows for the elimination of the influence of any surface effect which inevitably exists in concrete structures. In order to minimise the error in the derivation of in-situ stresses, an iterative method is established to deal with the redundant data recorded during the tests. A detailed example is given for the application of the present method to strain relaxation data from site measurements. The results show improved accuracy and efficiency of data analysis, and the capability for practical use.