The significance of hydrotropism in influencing the direction of root elongation in soil or similar media has been unclear hitherto. Tsuda et al. (pp. 767-770) demonstrate positive root hydrotropism can occur when a steep and stable gradient in water potential is applied across roots of the agravitropic mutant of pea growing in vermiculite. This finding demonstrates that hydrotropism is not restricted to air-grown roots.