SummaryFor artificially reconstituted aggregates of soils low in organic matter the definitions of the stability of structure in terms either of cation balance and cation concentration of the ambient solution or of the drainage moisture contentsuction relationship characteristic after slow wetting are consistent.Identified factors of organic matter and of heating and drying (or drying alone) confer a structural stability on aggregates which can be detected by the moisture characteristic method. There is circumstantial evidence to suggest that the organic matter must be in equilibrium with vegetation.Since more than one factor affect structural stability, and since any particular method of distinguishing between different degrees of this stability may not necessarily suit the range of stabilities presented, the independent identification of soils, known to behave with differing aggregate structural stability in the field, is not necessarily possible with any laboratory method which describes changes in structural stability.