Two similar experiments were conducted with winter wheat growing in pots of soil. Plants about 5 weeks old were placed in a growth chamber under constant conditions. On half of the plants 60% of the roots were cut at their origins; thus the root density was altered, but not the volume of soil. Half of these pruned pots and half of the unpruned were maintained at field capacity. The remainder were allowed to dry out to somewhat drier than —15 bars soil matric potential (this took 8 and 13 days in the two experiments), and the plants were then harvested. In the dry treatment root pruning did not reduce growth. There is some indication that root pruning increased growth in the dry treatment and reduced it in the wet; but this is not conclusive. When the mean of wet and dry treatments together is considered, root pruning had no detectable effect on either root or shoot growth. In the wet treatments root pruning reduced transpiration by about 25–30%. In the dry treatments as the soil dried out the relative difference in transpiration rate between pruned and unpruned plants decreased. This result differs from a previous expectation that root density would have more effect on transpiration in dry soil than in wet.