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In arid and semi-arid areas, drought and boron (B) toxicity are common deterrents to high crop yield. There seems to be an interaction of B toxicity with drought because B symptoms in the field often express under drought. This study examined the possible interaction of terminal drought and subsoil B on barley root growth and water use. A B-toxicity sensitive barley line was grown, in PVC tubes in a plastic house using a randomized complete block design with three replicates. There were two factors: water level (normal vs. terminal drought) and B level(+B vs. -B in the subsoil between 20-60 cm depth). No significant drought by B interaction was detected for soil water content and for all plant characters measured. The +B tubes held more water than the -B tubes from 100 days after sowing. High subsoil-B level reduced root dry weight in the whole profile except in the 2nd and 5th 10-cm sections. In contrast, terminal drought had no effect on root growth. Results indicate that if a high level of subsoil B exists, uptake of water and soil nutrients may be depressed in nearly the whole soil profile, not only in the subsoil alone. This means that breeding for drought tolerance alone may not be adequate; B-toxicity tolerance is needed as well. The absence of drought by B interaction indicates that the effects of high B levels can be studied under either terminal drought or normal conditions, and vice versa.