This paper presents a method that could diminish systematic errors of gamma techniques for assay ofradwaste drums. The idea is the combination of Segmented Gamma Scanning (SGS) technique and technique using two identical detectors. The results show that the maximum errors are small in comparison with those of SGS technique and technique using two detectors. This combinative method corresponds well to determine activity of radioactive in low density waste drums, such as organic materials: bags, protective clothing, shoes, gloves etc...