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The two-stage method belongs to the group of approximate methods of calculation of statically indeterminate systems because differences of the stiffness of component parts, joined in the same node, are not considered in this method. The paper presents a comparison between the values of forces calculated in the members of a selected type of statically indeterminate plane truss under load forces applied in a symmetrical way and in a non-symmetrical way. The comparison is drawn between values of forces calculated for the same trusses by the application of the two-stage method and by the application of suitable computer software. The values of the forces determined by the computer software are considered as exact results because in this case the stiffness differences of the component parts are taken into consideration. The point of the two-stage method is to remove, from the area of the statically indeterminate truss, a certain number of members which are equal to the statically indeterminacy of the basic truss. Appropriate statically determinate truss is calculated in each stage what implies, that is one of very simple methods, like for instance Cremona’s method, can be used for this purpose. The trusses calculated in each stage are of the same clear span and they have identical construction depth like the basic indeterminate truss, however they are loaded by forces of half values compared to forces applied to the basic one. The final forces in the members of the statically indeterminate truss are calculated as resultants of forces defined in each stage for members having appropriate positions in the area of the truss system.