Reinforced concrete frames are usually infilled with masonry walls but, in most designs, both the shear strength capacity of these walls and the contribution of the infill panel openings on the shear strength of the infilled frame, especially in critical cases of seismic loading are generally ignored. This paper reports the results of an experimental study of the influence of central openings in the infill on the sway stiffness of reinforced concrete plane frames. A series of 1: 4 scaled structural models with opening ratios from 0 to 50 percent in steps of 10 percent were designed, constructed and tested in the study to obtain the load-displacement profiles. The test results were validated with output of FE models of the prototype walls using SAP 2000 analysis software. The results confirm that 1: 4 model adequately reproduces the behavior of infilled frame with openings including lateral stiffness and anisotropy. The six percent accuracy of predicted shear strength of infilled frames under lateral loadings as a function of opening ratio is considered sufficient for engineering design purposes.