Intensive arable production normally involves an increasing frequency of cultivation, and hence an increasing probability of soil compaction, particularly if the soil is cultivated when it is wet. The effects on the potential ability of the soil to produce crops is uncertain, because the relations between soil physical conditions and crop growth are poorly understood. To measure damage requires improved techniques for measuring pore size distribution, as well as pore continuity and stability. Most damage takes the form of a reduction in the number of transmission pores (those greater than 0.05 mm, equivalent cylindrical diameter) although storage pores may also be lost in intensively cultivated soils. Where damage is primarily in the surface soil it can usually be repaired by appropriate cultivations. Where compaction of subsurface soil occurs, or blockage of subsurface pores by dispersion of clay from disrupted aggregates, the damage is less easily repaired. Soils differ considerably in their ability to withstand intensive cultivation. The behaviour of soil aggregates on immersion in water provides a useful guide to those likely to suffer more permanent damage, and those where increasingly intensive production can be safely practised.