Aggregates taken from sequential samplings of a range of red-brown earths showed a definite seasonal trend in relative stability. Maximum stability of the aggregates occurred in the summer, followed by a gradual decline during the autumn and early winter and an increase in the spring and early summer. In all phases of the crop-pasture rotation on all the red-brown earths, this trend was minimized by a combination of chemical treatments, designed to oxidize polysaccharides and polyuronides and to break the organic matter-polyvalent cation-clay bridge. The residual aggregate stability after the combined chemical treatment increased with the proportion of pasture phase in the rotation. Individually, the chemical treatments reduced the aggregate stability by a constant amount throughout all the seasons. The aggregate stabilizing mechanisms broken by the individual treatments make a constant contribution to stability throughout the year. This contribution increases with increasing cultivation in the rotation. In contrast, the aggregates taken from the solonized brown soil were stabilized by calcium carbonate. No seasonal trend or rotational effect was evident in these aggregates.