Cauliflower (Brassica oleracea L. var. Botrytis L. cv. Pusi) grown with 0·2, 0·4, 0·8, 2·0 and 4·0 mM K produced best growth and optimum dry matter at 4 mM K. Suboptimal K supply caused decrease in tissue concentration of K and produced visible symptoms of K-deficiency. Leaves of low K plants showed decrease in stomatal aperture associated with increase in stomatal resistance and decrease in transpiration. At the same time, their specific leaf weight was high and relative water content was low, indicating poor tissue hydration. Low K leaves also showed increased accumulation of proline. The magnitude of the K-deficiency effects was related to the severity of K-deficiency. Observations suggest poor absorption-transport of water under K-deficiency.