The paper presents principles of methods by Mitscherlich, Robinson and Nikolajew for the determination of maximal soil hygroscopicity (MH). Methods by the above-mentioned authors were modified and adapted for serial determinations. Modification of MH determination methods was found to simplify the course of investigations, increase repeatability of results and facilitate determinations of large sample series. The paper presents the need and possibility for MH determination not only of air-dry powdered (sieved through 2 mm mesh) soil mass but also soil aggregates of natural and modelled structures, air-dry and wet samples. MH was determined in a vacuum chamber of vacuum drier over saturated K₂SO₄ solution. The use and applicability of the method was presented on 10 soils of diversified texture and structure.