Tensile tests of plastically deformed specimens were performed in order to investigate the relation between variation of magnetic characteristics and residual plastic strain. Deformed steel (CSN 12050) specimens were investigated by the method of magnetic adaptive testing (MAT), measuring and evaluating series of minor magnetic hysteresis loops. It was shown that an efficient combination of the MAT parameters yields a reliable and unambiguous correlation with residual strain of the specimens even though all relations between the strain and each of the individual MAT-parameters were nonmonotonous.