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The extent of rooting and the water use of Guiera senegalensis bushes at a fallow savanna site in south-west Niger were investigated. Low root length densities were found up to the maximum sampling distance (8 m horizontally and 2 m vertically) from the base of the bushes. Changes in soil water content of the soil profile were monitored using a neutron probe at seven locations over a 20 m transect between two G. senegalensis bushes. During the 1993/94 dry season, a progressive drying front was observed moving away from a G. senegalensis bush both horizontally (up to 10 m) and vertically (up to 4 m). Mean water loss from the top 4 m of the soil profile over the 8-month dry season was 151 mm. This was attributed to water use by G. senegalensis, and comprised 28% of the 1993 total annual rainfall. Clearing fallow savanna land for millet production will result in increased deep drainage partly through reduced dry season water use by the deep rooted bushes. (C) 1998 Academic Press.